The fund-raising apparatus powering President Obama’s re-election effort has struggled to attract the big-money donors who contributed to Mr. Obama’s record fund-raising haul in 2008.

Mitt Romney, the presumptive Republican nominee, faces the mirror-opposite problem: the bulk of his campaign’s war chest has been built big check by big check, while small donations — defined as contributions of less than $200 — have been scarce, according to Federal Election Commission data compiled and analyzed by Derek Willis of The New York Times.

More than half of Mr. Obama’s fund-raising total has arrived in donations of less than $200. Just 13 percent of Mr. Romney’s fund-raising has come in such small denominations. Instead, a majority of the money Mr. Romney has raised arrived $2,500 at a time, the maximum campaign donation allowed for either the primary or the general election (an individual can contribute $2,500 to a candidate’s primary campaign and another $2,500 to the general election campaign).



Note: the above percentages apply to the total amount of money raised by each campaign, not the number of donations.

Mr. Obama has raised roughly $193 million; 19 percent of that sum, or $36.6 million, came from donations of $2,500. Of the $87 million the Romney campaign has raised, 57 percent, or $49.3 million, came in $2,500 chunks.

Of course, a dollar is a dollar, whether it reaches a campaign’s coffers alone or accompanied by 2,499 compatriots. And while Mr. Obama has raised significantly more money than Mr. Romney so far, the general election is just beginning. Moreover, spending by Republican-leaning “super PACs” is expected to far exceed spending by Democratic ones.

For the Romney campaign, however, a paucity of small-dollar donations is inauspicious not because it means that it will have trouble raising enough money (it probably won’t, and if it does, Mr. Romney has considerable personal wealth at his disposal). Rather, a lack of small-dollar donors could indicate tepid support for Mr. Romney among the Republican base.

Research by Adam Bonica of the political science department at Stanford University suggests that small donations tend to come from the wings of the ideological spectrum. For Mr. Romney, donations of less than $200 would most likely come from the most conservative camp in the Republican Party, a group that resisted his candidacy throughout the nominating process.

“In the primaries, there were a lot of small donors, but they weren’t giving to Romney,” Professor Bonica said. “I think it does have something to do with Romney being perceived to be more moderate.”

The Romney campaign’s continuing dearth of small-dollar contributions suggests that very conservative voters, like those who supported Rick Santorum and Newt Gingrich, have yet to warm completely to Mr. Romney, which could potentially mean not only less money but also fewer lawn signs and bumper stickers, fewer volunteers and, ultimately, fewer votes.

It is too early to call the problem chronic. The Republican primary was only recently resolved. Mr. Gingrich is expected to drop out of the race officially on Wednesday. Mr. Gingrich, as well as Mr. Santorum and Michele Bachmann, who appealed to more conservative voters, will presumably endorse Mr. Romney eventually. And at that point, conservative Republicans may begin coalescing around Mr. Romney in earnest, enabling his campaign to construct a robust small-donor network.

Small signs of this transition are already apparent. As the Republican primary progressed — and it became clearer and clearer that Mr. Romney would prevail — the cumulative share of his fund-raising coming in checks of less than $200 inched upward, albeit very slightly.

The most recent quarter (January through March) was Mr. Romney’s most successful in terms of small donors. He raised twice as much in donations of less than $200 than in his previous best quarter, the last quarter of 2011. That may be a sign of things to come, as conservatives committed to defeating Mr. Obama come around to supporting Mr. Romney.

“I would expect to see an uptick in the amount of small donations the Romney campaign is getting, but I don’t expect it to be anywhere near Obama’s level,” Mr. Bonica said.