When he announced in June that he would not be taking public funds for his general election campaign, Barack Obama justified the decision — a seeming reversal of his earlier position — by arguing that his broad base of small-money donors had altered the basic landscape of presidential campaign finance. The presumed Democratic nominee contended that his record-shattering fundraising operation amounted to a “parallel public financing system, where the American people decide if they want to support a campaign they can get on the Internet and finance it.”

Commentators disagreed on how effective that rationale was in deflecting criticism of Obama’s change of heart. But few have challenged its underlying premise: that his campaign has harnessed the Internet as never before to democratize the role of money in politics. Indeed, the general run of commentary has hailed Obama’s online gold rush as nothing short of a revolution in how candidates and parties of all stripes are compiling cash for their campaigns.

But if a revolution has happened, it’s largely news to the campaign finance system. The Internet has indeed altered the nature of many donor transactions — for the givers and the campaigns alike. But the system has so far registered the effects of that change unevenly.

Beyond the high-profile presidential contests, the traditional big-money donor profile is largely holding fast. What’s more, the demographics of the smaller-money contributors, who prefer the Internet more and more, bear some striking resemblances to their flusher counterparts, who traditionally have delivered their money at cocktail receptions. Recent studies show that political donors who give online are still overwhelmingly wealthy, highly educated, older and white.

The most frequently cited figure in campaign finance circles is also one of the smallest: 2 percent. That’s roughly the portion of the adult American population that gives money to campaigns. And this group skews strongly toward the top end of the socioeconomic spectrum, because they have the discretionary income to push their political agendas.

The Internet has upended that dynamic in important ways, allowing candidates to reach out to a much broader pool of potential donors and giving voters a powerful tool for actively seeking out potentially suitable candidates, rather than waiting for a direct-mail flyer or an embossed invitation to a ballroom event. In 2006, George Washington University’s Institute for Politics, Democracy and the Internet issued a report on giving in the 2004 presidential campaign that found that “almost half of small online donors contacted the campaign first.”

The movement toward a self-selected online donor class has also contributed to the marked rise in small-amount donors to presidential campaigns — generally characterized as those who give $200 or less, because that’s the threshold below which the names and occupations of donors need not be disclosed to the Federal Election Commission. The size of that group tripled between 2000 and 2004, and is expected to show similar growth for this year. “The trend is those online donations are coming in smaller amounts,” said Julie Germany, who runs the George Washington University institute.

Without question, the Obama campaign has made the most of the dramatic upticks in both online and small-denomination giving. Its enormous army of small donors has yielded impressive cash gains: $30.8 million in gifts of $200 or less in June alone, more than half the Illinois senator’s $52 million haul for the month. And once those donors have been roped in, the campaign has made every effort to keep them engaged with an array of community-based forums and activities, ultimately leading to many repeat donors.

By the end of June the Obama campaign reported it had raised slightly more than half of its primary money from individual donors in amounts of $200 or less, an impressive amount for a top-tier, mainstream candidate. But it also had relied on contributions of $1,000 or more for about a third of those individual-donor receipts and had to court those big-ticket donors assiduously in the formative stages of his campaign for the Democratic nomination, before the online operation began to yield significant money. (All the other principal presidential contenders have raised at least half of their money in checks of $1,000 or more. Obama’s fall opponent, Republican Sen. John McCain of Arizona, has raised a quarter of his primary election funds in small donations and three-fifths in big gifts.)

What’s more, while Obama and his backers contend that their small-money, mostly online donors reflect the demographics of the nation, studies suggest otherwise.

The George Washington study concluded that small-amount givers — defined as those contributing $100 or less to a campaign — four years ago weren’t quite as posh as the big-amount donors but were still far removed from a pink-and-blue collar profile: Twenty-nine percent reported household incomes of $50,000 or less, but 33 percent had earnings of $100,000 or more. More than half had some graduate-school education, and three in five were men. “Small donors look more like middle-class Americans in terms of their education and household income, although donors are still higher in both respects,” the report concluded.

A comparable analysis of donors to the 2000 presidential campaigns, by Georgetown University government professor Clyde Wilcox, drew much the same conclusion.

The small-donor boom is also not the “youthquake” in American politics it’s often advertised to be. George Washington researchers found that the small donors’ median age was actually higher than that of big-money donors. The reason, evidently, is that small donors are “more congregated at both the young end (ages 18 to 34) and the old end (over 65) of the scale,” they reported. The researchers did, however, find that young people rarely gave by mail or in person, whereas three-quarters of donors 65 and older had.

“Young donors are seven times more likely to give over the Internet,” said Michael Malbin, the director of the nonpartisan watchdog group the Campaign Finance Institute — but even then, they don’t add up to a majority of online donors.

The Obama campaign is likely to bring the demographic profile of online and small donors closer to Earth, since it has greatly energized African-American and younger activists, many of whom had not previously donated money or time to a campaign. But as Malbin cautions, it’s hardly realistic to expect a social revolution in political giving patterns, given the overall composition of the donor class. The important thing to note, he says, is that political giving is “no longer the exclusive domain of the rich. That is a major change by itself.”

For politicians outside the presidential orbit, meanwhile, the online wave of small-donor money looks more like a trickle. Through March 2008, House candidates had raised less than 10 percent of their overall funds from small-money donors, the Campaign Finance Institute estimates — a share that’s “virtually unchanged” from past campaign cycles, the group said in a report in May.

A big reason for the stasis is the power of incumbency. “The typical incumbent member of Congress is able to raise more than enough money to fund a normal campaign by going to people who can buy high-price tickets to events in Washington,” Malbin said.

Challengers can exploit the Web to chip away at that advantage, but doing so requires a concerted effort. “It takes time to cultivate an e-mail list, to build a network organically and to grow an online fundraising community,” said Marissa Doran, director of strategy and communications for the Democratic national fundraising site ActBlue. “Not every campaign has made that initial investment.”

According to Malbin, the handful of congressional candidates who are able to tap into the Internet’s fundraising potential tend to be running insurgent-style campaigns or have acquired an enhanced national profile thanks to the blogosphere or online interest groups. Liberal Democrats such as Darcy Burner, a former Microsoft Corp. manager who is challenging Republican Dave Reichert’s bid for a third term in the wealthy Seattle suburbs, and Donna Edwards, who came to Congress this summer after defeating Albert R. Wynn in a primary in the Washington suburbs of Maryland, are prime examples of this type of candidacy. Both have raised more than $400,000 on ActBlue.

Those success stories point up another feature of the online fundraising world: Democrats enjoy a clear advantage. According to Doran, last year ActBlue used the Web to raise $16.5 million, three-quarters of which went to fund House and Senate campaigns. There are a few counterpart Republican sites, but the largest one, Slatecard.com, lags far behind, with $442,000 raised for all candidates this election cycle. “Republicans are behind the curve of fundraising online, and they’ve known that for a while,” said Dallas McKellips, the campaign manager for Matt Salisbury, who made the Internet central to his fundraising efforts in a losing bid to defeat freshman Rep. Bill Sali in Idaho’s Republican primary.

But, he added, “I think that with next generation of candidates you will see the Internet becoming more and more powerful, not just among Democrats, but Republicans as well.”

Indeed, as Malbin noted, politicians are an imitative breed. In the next set of races, “you can be sure all the campaign managers will be reading up on what happened in 2008,” he said. “They won’t all be equally successful, but they’ll all be looking at this.”

FOR FURTHER READING: Fundraising strategies, CQ Weekly, p. 1160; McCain and Obama’s public-financing positions, p. 600.