Landmark housing legislation could be on its way to President Bush by the end of the week after the House passed the package Wednesday and Senate leaders quickly moved to take it up.

Lawmakers and the Bush administration, which dropped its remaining objections to the bill (HR 3221), hope its passage will reassure the housing market enough to avoid triggering one of the bill’s key elements — a bailout of Fannie Mae and Freddie Mac.

“Basically, this sends a signal to the markets that will help calm the markets — that we’re not walking away, that we’re going to be involved,” said Sen. Richard C. Shelby, R-Ala., a key architect of the measure.

Shortly after the House voted, 272-152, to send the measure back to the Senate, Majority Leader Harry Reid, D-Nev., filed for cloture and engaged in a parliamentary maneuver that would block amendments, saying he expected votes on the measure Friday.

But a threatened objection from Sen. Jim DeMint, R-S.C., could force final passage to be delayed until Saturday.

The package — which also includes an expansion of a federal mortgage refinancing program, a housing-related tax package and major regulatory changes — marks the single most significant congressional response to the ongoing crisis in the residential housing sector and wider financial markets. Rising foreclosures and slumping share prices for mortgage financiers Fannie and Freddie have spooked investors, lawmakers and regulators and spurred Congress to action.

But significant pockets of resistance remain, and a rare fissure opened between congressional Republicans and the White House. Only 45 House Republicans voted for the bill, and conservatives in the Senate continued to grumble.

“I’m deeply disappointed the White House will sign this bill in its current form,” said House Minority Leader John A. Boehner, R-Ohio. “We must take responsible steps to ensure our financial and housing markets are sound. But the Democrats’ bill represents a multibillion-dollar bailout for scam artists and speculative lenders at the expense of American taxpayers.”

The legislation picked up significant momentum on Wednesday when the Bush administration reversed course and dropped its final objections to the bill, while key Senate lawmakers also endorsed the House-passed measure.

The legislation includes authority, sought by the administration, for the federal government to take an equity stake in Fannie Mae and Freddie Mac and offer them a bigger credit line if their finances deteriorate further. The authority, which would expire at the end of 2009, would not include a dollar cap but would be subject to the federal debt limit.

The credit line troubled many conservatives. “Apparently the president has decided he wants this bailout more than he wants to stand by his original position that he would veto it,” DeMint said. “If they’re going to send us bad policy . . . we’re at least going to have the 30 hours of debate. . . . To say that we’ve got to pass it in 10 minutes on the floor without reading it, which is what they’re going to ask us to do, that’s not going to happen.”

DeMint would like to offer an amendment that would ban lobbying and other political activity by Fannie and Freddie, which have significant clout on Capitol Hill.

Reid acknowledged that a handful of conservative Republicans may slow the measure’s progress and force the Senate to overcome procedural hurdles before clearing the bill. Still, the package is expected to draw broad support in the upper chamber.

“I don’t think it can be derailed,” Reid said. “You can slow it up a little bit. I hope we can finish it.”

The bill also includes a new regulator for Fannie and Freddie; an overhaul of the Federal Housing Administration, an agency that insures mortgages; an FHA-led program to help borrowers refinance mortgages they at present can’t afford; and $15.1 billion in tax breaks.

The measure would offer a one-time tax credit to most first-time homebuyers that is equivalent to an interest-free loan for 10 percent of the home’s cost, up to $7,500. The credit would be available until July 1, 2009.

The package would also allow taxpayers who do not itemize on their returns to claim a one-time $500 deduction for local property taxes.

Senate Banking Chairman Christopher J. Dodd, D-Conn., and Alabama’s Shelby, the ranking panel Republican, gave their blessing to the package Wednesday, saying they did not intend to alter it. They have spent weeks hammering out the final version with House Financial Services Chairman Barney Frank, D-Mass.

“This legislation will take several steps which we believe will help address the causes for the current crisis,” Dodd said at a joint press conference with Shelby. “As some have said, this is the most important piece of housing legislation in a generation.”

Shelby said the legislation could prove essential for Fannie and Freddie to weather the current financial storm.

“Without this legislation . . . I don’t know if they could survive,” he said. “We need to make sure [they do], because there’s a lot at stake.”

The administration also threw its full weight behind the measure.

“While this bill should have been improved, the temporary Treasury authorities and GSE [government-sponsored enterprise] reform provisions are too important to the stability of our Nation’s housing market, financial system, and the broader economy not to be enacted immediately,” the White House said in a statement of administration policy.

White House Deputy Press Secretary Tony Fratto said that Treasury Secretary Henry M. Paulson Jr. recommended the president sign the legislation because it includes the regulatory overhaul of Fannie and Freddie long sought by the administration, as well as Paulson’s proposal to backstop the troubled companies.

“The positive aspects of the bill are needed to increase confidence in the financial markets,” Fratto said. “These are new authorities [Paulson] said he needed.”

Lately, the White House had centered its veto threat on a provision to provide $3.9 billion in grants to states and localities for the purchase and rehabilitation of foreclosed homes. Administration officials complained that the program would simply benefit lenders, not individuals.

Fratto continued to criticize it but said, “We’re in a position where we are going to have to accept some bad policy.”

Frank said: “I don’t like everything in this bill either. It is inconceivable to me that anybody would like everything in this bill — it is a product of a very significant set of compromises.”

Final details of the bill came together Tuesday.

While the package will not include a dollar limit on the Treasury’s lending or equity purchases, any spending will be subject to the statutory debt limit. The legislation includes an $800 billion increase in the debt limit for all government obligations, pushing the ceiling to $10.6 trillion, as previously planned.

Under the measure, the government will have control over the compensation packages for Fannie and Freddie executives, which some critics say are too high. Although the legislation will not mandate preferred-shareholder status for any government equity stake in the two companies, which would ensure a priority return on a federal investment, that will be an option the Treasury secretary could use if the lifeline is activated.

The legislation would give the Federal Reserve a “consultative” role to the new regulator for Fannie and Freddie. But that provision would expire at the end of 2009 under the House bill. The administration proposal would not have sunset the Fed’s role.

The cap on the size of mortgages that Fannie and Freddie can buy and package as securities, known as the conforming loan limit, would be set at the lesser of $625,000 or 115 percent of an area’s median price in certain high-cost areas.

The measure includes some $18.5 billion in offsets, which would cover the cost of the housing tax breaks as well as most of the cost of the $3.9 billion in grant funding for states and localities.

The Congressional Budget Office (CBO) said Tuesday that the temporary lifeline for Fannie and Freddie could cost the federal government $25 billion over the next two fiscal years, though it added that chances are “probably better than 50 percent” that a bailout won’t be necessary.

Bart Jansen and Frank Oliveri contributed to this story.