Moderation hasn’t been a byword of the Bush era, and so the moderates of Congress haven’t really had much to do but sit off to the side and endure the wary stares of their colleagues in the Republican or Democratic mainstream.

Sure, some of the centrists got courted once in a while, usually when the party leaders or the president decided there was really no way to get a deal without them. But during a period when the voting has been as partisan and the debates as polarizing as any in modern times, lawmakers close to the ideological middle mainly felt dealt out and distrusted. A few of them — James M. Jeffords most famously — simply dropped their partisan tags altogether in a bid for relevance, or at least respect. Others were swept out of office or chose to give up and go home.

That’s all starting to change, and the inauguration of the 44th president looks to herald a golden time for the centrists. The signs are as clear as the passenger manifests on the campaign planes: Republican Sen. Chuck Hagel of Nebraska tagging along with Barack Obama last week, independent but formerly Democratic Sen. Joseph I. Lieberman of Connecticut in the shadow of John McCain for the past several months.

Like so many candidates have before, Obama and McCain are promising to restore a more collegial tone and a more bipartisan approach to Washington. But each of them seems to hold the genuine prospect of fulfilling that goal in the White House, because each has a history of working across the aisle, and also because the start of a new administration is historically the ripest time in Congress for collaboration.

“Moderates have tried to drive the debate, and at times we have, but more recently it’s been driven more by left or right than it has by moderates,” said Nebraska’s Ben Nelson, who voted more often with President Bush and less often with his own caucus than any other Senate Democrat last year. “There’s an increasing role for us in the days ahead.”

The moderates are already preparing for that period of opportunity and influence. They know it won’t come this fall, when the calendar is short and there seems to be no campaign season imperative for legislative accomplishment. But the centrists are confident that gasoline prices will still be climbing, the ranks of the medically uninsured will still be growing and federal spending on entitlement will still be increasing come January. And so several bipartisan clusters of moderates, in the Senate in particular, have been quietly talking strategy and batting around proposals they hope will catch the attention of the next president.

“If you want to put an issue at the top of a president’s in-box, which is already filling up fast, you have to have a bipartisan group that’s already working on a solution,” says Oregon’s Ron Wyden, who’s leading seven other Senate Democrats and eight Republicans in search of a centrist compromise on universal health care coverage.

But for either Obama or McCain, paying heed to lawmakers from the other party will be more than a nicety. It will be a necessity. That’s because, while the Democrats seem certain to expand their majorities come November, their gains probably won’t be such that party leaders can rely only on their own members to advance a legislative agenda — regardless of who’s president.

In the House, 10 or more of the likeliest Democratic freshmen next year will be moderates who either defeat centrist Republicans in November or pick up seats left open in this year’s wave of GOP centrist retirements. And these newcomers will only add to the strength of the fiscally conservative Democrats who have often made life complicated for Speaker Nancy Pelosi in the past two years.

In the Senate, Democrats are now confident they’ll pick up between four or five seats and have a shot at a handful more beyond that. Even the most optimistic result, however, would almost certainly put the party’s effective majority a vote or two shy of the magic 60 — the number of votes necessary to shut down a Republican filibuster.

That means Majority Leader Harry Reid, whether he’s inclined to or not, will need to look to win over at least a couple of GOP moderates on many of the most pivotal votes. Pressing him to cut such deals, especially if Obama is president, will be Richard J. Durbin — Reid’s deputy and would-be successor, as well as Obama’s closest associate in the Senate. (Durbin, p. 2052)

“There’s an expectation that the new president will reach out,” said David King, a public policy lecturer at Harvard’s Kennedy School of Government. “But it really all comes down to whether you have 60 votes.”

Indeed, the exact outcome Nov. 4 — whether McCain or Obama is elected along with a more Democratic Congress, and just how many more Democrats get elected — will set the parameters for which moderates move more clearly to the forefront next year.

Republican centrists would stand to wield more influence in the first years of an Obama administration. He’s had a generally liberal record and has been a reliable Democratic vote during his 43 months as an Illinois senator, of course. But as president he’d be under considerable pressure to exercise his mandate to deliver “change we can believe in” with proposals that had as broad and bipartisan appeal as possible. And that means moderate Republicans should be permitted to insert themselves and put their own stamps on at least the margins of the Obama agenda — even at the risk of frustrating congressional liberals, who say they’re hoping to be the center of attention if there’s a Democratic president and stronger congressional majorities.

Democratic centrists will expect to have more sway if the next Congress is working with a President McCain. He’s been among the Republicans most likely to operate from the center and find Democrats to partner with during his career representing Arizona in the Senate. If as president he tried to advance his current views on some of the most nettlesome issues, such as immigration and climate change, he would probably look to advance his agenda with a coalition of middle-of-the-road Democrats and not-all-that-conservative Republicans. Many in the bloc of fiscally conservative House Democrats would also hurry to his side if McCain pushed his campaign to curtail “wasteful” domestic spending.

But Republican centrists, too, would probably get much more attention than they do now — even at some risk, for McCain, of further threatening his already tenuous relationship with the conservative wing of his party.

Moderates emerged as a force in two very different ways at the start of the current and the previous presidencies.

When Bill Clinton took office in 1993, there were such solid Democratic congressional majorities — 258 seats in the House and 57 in the Senate — that he was able to push through his initial agenda without making any real overtures to moderates in either party. They voted for his more centrist proposals anyway; when the GOP abandoned him entirely on his signature deficit reduction effort, Clinton twisted enough arms, all in his own party, to squeak by with the bare minimum of support. It was only when most fellow Democrats abandoned him, on the North American Free Trade Agreement at the very end of that year, that free-trade moderate Republicans and Democrats stepped in and provided the margin of victory.

But moderates, Democrats especially, were central to George W. Bush’s first big victory in 2001, enactment five months after he took office of the deepest tax cut in a generation. Republican control of Congress rested on the thinnest edge at the time: the tie-breaking vote of Vice President Dick Cheney, with Vermont’s Jeffords about to bolt the GOP and deliver Senate control to the Democrats. And so the Bush White House told the top Republican tax writers to cut a hurry-up deal with two of the most prominent Democratic centrists in the Senate, Max Baucus of Montana and John B. Breaux of Louisiana. The deal they struck was a smaller tax cut than Bush wanted, with the benefits targeted more toward low-income people than he’d proposed. But only two Republicans in all of Congress voted against it — McCain was one of them — and a dozen Democratic senators and 28 Democratic House members voted for it.

The 50-50 Senate that helped give rise to that deal hasn’t been replicated since, but neither has there been a period when one side could control Congress without any help at all from the other party. In fact, the last filibuster-proof majority in the Senate belonged to the Democrats three decades ago, from 1975 through 1978; the party then also enjoyed a huge House majority.

Any time when one side must rely on the other for victory is ripe for the moderates to assert themselves. The current era, when the partisan impasse has become the default setting at the Capitol, only magnifies the opportunities for people who can come up with bipartisan solutions. “It’s the only way to get something done around here,” says Democrat Kent Conrad of North Dakota.

Conrad, fellow Democrat Mark Pryor of Arkansas and Republican Saxby Chambliss of Georgia, along with seven other senators from both the parties, are now in search of just such a bipartisan package to address energy prices, an issue that has become highly partisan and nearly impossible for the leadership to tackle. A similar effort is under way in the House, where a dozen lawmakers from each party have joined an ad hoc caucus formed by Democrat Neil Abercrombie of Hawaii and Republican John E. Peterson of Pennsylvania.

The only precondition for the House groups is that its member support a resumption of offshore drilling as a way to boost supplies. For its part, the Senate group is coming at the issue from all angles: renewed drilling, promotion of alternative fuels and a crackdown on oil speculators are all options on the table, Conrad says. But the thread that binds the coalition is a deep interest in boosting local economies and industries. North Dakota, for example, could benefit from increased oil shale production and coal mining.

It’s highly unlikely that either bipartisan energy group, or the Wyden health care group, will be able to advance its proposal this year. But that’s not really the objective, says the leader of a third such effort: Republican Sen. Judd Gregg of New Hampshire, who’s working with members of both parties, on both sides of the Capitol, to push the idea of creating a joint congressional-administration commission to propose solutions to long-term budget problems, such as the growth in entitlement spending.

“We’re trying to create the memo that will control the message in the new Congress,” says Gregg. “We’re laying the groundwork.”

Such issue-based alliances will be popular in the Senate next year, said John J. Pitney, a politics professor at Claremont McKenna College in California. “There will not be a regular Gang of 14,” he predicted, referring to the bipartisan group of senators, organized by McCain, that diffused a potentially cataclysmic confrontation over judicial nominations three years ago. “It will be more of a pickup team,” he said, coalescing around issues, many of them regional, that draw senators from both parties together.

Those are the sorts of groups that either a President McCain or a President Obama could work with to advance his own agenda.

For example, the promotion of renewable fuels could win support in both parties, as long as lawmakers weren’t won over by community organizations that didn’t want the wind turbines, solar panels and other infrastructure in their backyards, says Frank Maisano, an energy communications specialist at the lobbying and law firm Bracewell & Giuliani. Building capacity for more ethanol, wind power and other alternatives would satisfy any number of Republican and Democratic members, especially those who believed their state or district could benefit financially from production, he said.

Overhauling the health care system will probably have to be done piecemeal if there’s an Obama administration, largely because it will be too difficult to assemble a majority behind a single, comprehensive package, said Robert Blendon, a professor of health policy and politics at Harvard. Efforts to increase funding for the National Institutes of Health, boost spending on health and safety regulators, and provide financial incentives for covering those who now lack insurance will all spark Republican complaints about runaway spending, Blendon said, but that opposition may be tempered by those GOP moderates who are willing to support increased funding for some health care priorities as long as other health spending is held at bay.

“Moderates will be deciding how much spending will go,” Blendon said. “Their numbers will be small, but they will be enormously important.”

Finding much centrist GOP support for his plans to withdraw U.S. forces from Iraq during the first 16 months of his presidency would be far more difficult for Obama, because the fault lines in the debate over the war have fallen so much along party lines, said James A. Thurber, who directs American University’s Center for Congressional and Presidential Studies. Most Republicans will be loath to reassess their support for the war unless the party’s losses this fall are more significant than expected and those lawmakers who survive conclude that they need to modify their views or risk losing in 2010.

Having the White House and the Capitol controlled by the same party may seem like a guaranteed winning combination for the people in both buildings, but it hasn’t always worked out that way. In 1994, Clinton bet much of his political capital on being able to sell his health care initiative to a solidly Democratic Congress, completely misunderstanding how many moderates in his own party hated his ideas and were willing to join with virtually everyone on the Republican side to bury his ambitions. After those same Democratic moderates helped hold hostage Clinton’s other priority that year, an anti-crime package, the party’s apparent disorganization and discord fueled the Republican takeover of Congress in the election that fall.

Obama could find himself in a similar fix, having to manage newly empowered Democrats with their own policy priorities and having to prevent divisions in his own party that threaten to sabotage his plans. That thought isn’t lost on centrist senators such as Delaware Democrat Thomas R. Carper, who believes the only way to avoid a train wreck reminiscent of the early Clinton years is to let moderates call the shots.

“The last time the Democrats were in the majority of the House and the Senate and we had a Democratic president . . . were not good years for our party,” Carper said. “We need to remember a lesson that we didn’t remember then: For our party to be successful, we need to govern from the middle. We can’t govern from the far left or the far right.”

If he’s elected, McCain will be expected to turn often to his fellow centrists in the Senate to provide a margin of victory for his agenda — hoping, as he campaigns this fall, that as many of them as possible are still in office for the 111th Congress.

McCain’s most significant recent legislative triumph, an immigration policy overhaul combining border security enhancements with a guest worker program and a path to citizenship for illegal immigrants, passed in 2006 with the votes of 39 Democrats and 22 other Republicans. Only half of them are sure to be back next year. Seven have already left or are retiring; the other four — Susan Collins of Maine, Norm Coleman of Minnesota, Gordon H. Smith of Oregon and Ted Stevens of Alaska — are all in highly competitive re-election races.

The only Democratic incumbent in a competitive re-election race this year is also one of the party’s most prominent moderates, Mary L. Landrieu of Louisiana. She also voted for that immigration bill.

Support from such centrists would be essential to McCain’s prospects of reviving such a proposal as president, which would require him to repair a significant intraparty rift. He might have more luck, among rank-and-file Republicans and Democrats alike, if he moved to open the oceans to oil and gas exploration, an idea about which he changed positions, endorsing it last month. The GOP has long called for more domestic production, and that plan isn’t dead on arrival with Democrats either, at a time of $4-a-gallon gasoline. Even Reid has suggested that his party could support offshore drilling as long as it was paired with substantial efforts to boost renewable fuels.

But beyond energy and McCain’s drive for spending restraint, there appear to be few obvious areas at the moment where his proposals would be embraced wholeheartedly by the Republican caucuses in Congress. And, Pitney notes, McCain could otherwise have a difficult time building coalitions, given his lukewarm relationship with the Senate minority leader, Mitch McConnell of Kentucky.

That means McCain would need to devote special energy early on to enlisting emissaries in the Capitol, said Candida Wolff, who became a lobbyist with Hogan & Hartson this year after three years as the chief lobbyist for the White House. “McCain should be asking himself, ‘Who is your champion?’ It’s better to keep Lindsey Graham in the Senate as a go-to person,” she said, pointing to one of McCain’s closest allies in the Senate, a South Carolina Republican often mentioned as a likely Cabinet secretary in a McCain administration.

Would GOP moderates be shunned by their more mainstream conservative colleagues next year if they teamed up with McCain and the Democrats on some issues? It’s too soon to tell, says South Dakota’s John Thune, a chief deputy whip for the Senate Republicans. But that’s not to say the GOP isn’t already considering the reality of having to dig in its heels even if it has one of its own in the White House.

“We’ll be very committed to making sure that our principles are asserted and that we get votes on amendments that we care about, and we have an opportunity to influence legislation,” said Thune. “I don’t know if that’s going to change whether we’re 49 or 45 or 48.”

If the Senate is where ad hoc, issue-based allegiances form — and where a handful of lawmakers going against the partisan grain can make a difference — the nature of the House means that centrists need to form somewhat sizable blocs to make a difference. Two of the most venerable such groups, the fiscally conservative Blue Dog Democrats and the socially moderate Tuesday Group Republicans, both say they are preparing to wield influence next year by putting a single-minded focus on fiscal discipline by the next president and the next Congress. Principally, that will involve pushing the Democratic congressional leadership to live by the pay-as-you-go budget rules they imposed last year, which require Congress to offset the costs of new mandatory spending initiatives or tax cuts with spending cuts or tax increases.

“No legislation, good or bad, will be passed without the Blue Dogs,” asserts Charles W. Stenholm, a lobbyist at Olsson Frank Weeda who as a Texas congressman helped found the group in 1995. “Anything they support will pass.”

Indeed, the 49-member group was on the party leadership’s mind this spring during final negotiations of the new farm bill. Knowing that the Blue Dogs, many of whom represent farming districts, wanted to increase funding for nutrition programs and preserve crop subsidies but would not embrace the extra spending without offsets, Pelosi persuaded Ways and Means Chairman Charles B. Rangel to include an extension of customs user fees in the farm bill, even though he’d hoped to dedicate that revenue to some of his own priorities. (The House’s budget hawks haven’t been able to preserve the pay-as-you-go principle every time. Last year’s law loosening of the reach of the alternative minimum tax in 2007, at a cost of about $50 billion, was enacted without offsets at the insistence of Senate Republicans.)

But the leverage of such centrist Democrats could be enhanced next year, when their roster seems certain to grow. At least 10 fiscally or culturally conservative Democrats are waging competitive contests for seats now held by Republicans. And already this year, conservative Democrats have won special elections to pick up three seats left open in midterm by Republicans: Bill Foster replacing former Speaker J. Dennis Hastert in Illinois, Travis W. Childers replacing Roger Wicker when he became a senator from Mississippi, and Don Cazayoux in place of Richard H. Baker in Louisiana.

With that trend in mind, Blue Dogs say they’re likely to add more members next year and work more closely with their Republican counterparts, the Tuesday Group, who now number 38. It’s an alliance that could pose some problems for the majority leadership, said Breaux, who now runs a lobbying firm with former Senate GOP Leader Trent Lott.

“If you have a lot more moderates and conservatives that stick together, you shift leadership,” Breaux said. Pelosi and her team, he said, will have to choose between pushing a more liberal agenda to their liking or appeasing budget hawks for fear of losing their support on any number of issues, particularly on expensive items such as a health care overhaul, changes to the tax code or climate change legislation.

For obvious reasons, Republican moderates will be the more powerful House bloc if McCain becomes president, says Mark Steven Kirk of Illinois, a co-chairman of the Tuesday Group. Like most in that group, McCain has long emphasized his desire to hold domestic spending in check and lower trade barriers. But the political fortunes of the Tuesday Group are the opposite of the Blue Dogs’: Several members, Kirk among them, are in tough re-election races, and a handful more are retiring from seats that could go Democratic.

If Obama wins, he will share Pelosi’s challenge: Adopt a relatively moderate agenda — one that will have a better chance of passing in the Senate — or build good will with liberals who supported his candidacy early on. Rep. Jim McGovern of Massachusetts, who voted with his party 99 percent of the time last year, is hoping Obama will choose the latter option. Tempering the Democratic agenda will prevent the party from moving forward, he said.

“I want health care for everyone, I want to end the war in Iraq, I want to deal with the issue of global warming, so my hope and desire is that we’ll have a very liberal Congress,” McGovern said. “I’m under no illusion that the world will get better overnight, but I think we need big, bold dramatic change.”

FOR FURTHER READING: Hagel, p. 2024; Peterson’s draft energy bill, p. 2058; independent voters, CQ Weekly, p. 1604; liberals’ agenda, p. 1520; farm bill (PL 110-246) offsets, p. 1110; McCain and the GOP, p. 354; Obama and McCain voting records, p. 124; immigration, 2006 Almanac, p. 14-3; Bush’s first tax cut (PL 107-16), 2001 Almanac,p. 18-3; Clinton’s first years, 1993 Almanac, p. 3, 1994 Almanac, p. 3.