Restore Our Future , the super PAC supporting Mr. Romney, spent more than $12 million in February, most of it on advertisements attacking his rivals as he battled in seven primaries and caucuses that month, according to campaign filings released on Tuesday. That followed close to $14 million in spending on Mr. Romney's behalf in January.

The group raised about $6.4 million — more than some of the candidates — from businesspeople and entrepreneurs who have long financed conservative causes, along with a small group of Wall Street executives who are also among top donors and fund-raisers for Mr. Romney's campaign. Nearly half of that amount came from a single donor: Bob J. Perry, a Texas homebuilder who is among the leading Republican donors in the country and who has financed groups like Swift Boat Veterans for Truth , an independent group that broadcast advertisements against Senator John Kerry , the Democratic presidential candidate in 2004.

Two other donors gave half a million dollars each to Restore Our Future: A. Jerrold Perenchio, a former chairman and chief executive of Univision, and David Humphreys, a Missouri businessman. Eleven donors gave $100,000, among them Harold Simmons, the leading super PAC donor in the country; Ken Griffin, an investor with the Chicago -based hedge fund Citadel ; Griffith Harsh IV, the husband of Meg Whitman , a former chief executive of eBay ; and Henry Kravis , a leveraged buyout investor.

A super PAC helping Mr. Gingrich, Winning Our Future, reported $5.5 million in contributions from Sheldon Adelson , a casino billionaire, and his family — more than twice as much as Mr. Gingrich raised himself — bringing their total contributions to the group to close to $16 million. Mr. Simmons, who has given to multiple candidates and super PACs, also gave the group $100,000. The group raised a total of $5.7 million in February.

The Red White and Blue Fund, which backs Mr. Santorum, raised $2.9 million in February, the bulk of it from three donors: William J. Doré, an energy executive, and Foster S. Friess, a mutual fund investor, who have been mainstays of the group's fund-raising this year; and Annette Simmons, the wife of Mr. Simmons, who gave $1 million.

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Endorse Liberty, a super PAC supporting Representative Ron Paul of Texas, had a steep decline in donations. After raising $2.4 million in January, the group took in just $282,466 in February and barely spent any money. Peter Thiel, a PayPal co-founder who anchored the group's fund-raising in previous months, did not contribute any money.

Mr. Paul, who has reliably drawn millions of dollars in small checks from his grass-roots supporters without winning a single nominating contest, is also facing a fund-raising slowdown, collecting $3.3 million in February, more than a million dollars less than what he raised in January. He began March with about as much cash on hand as Mr. Gingrich.

The candidates' declining balances — and the prospect of a long and exhausting primary season — have forced their campaigns to be more strategic about their advertising spending. In states like Georgia , Idaho and Ohio , total spending by super PACs has outstripped spending by the campaigns themselves, and that trend appears to be continuing into March.

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In Illinois , Mr. Romney spent about $1.1 million on advertising through last Tuesday, according to a media strategist who tracks ad buying, while Restore Our Future spent $2.5 million. The Red White and Blue Fund spent about $310,150, slightly more than the $215,726 that Mr. Santorum's campaign spent.

Leading up to the Mississippi primary last week, Winning Our Future spent almost $250,000 on advertising supporting Mr. Gingrich, while the candidate's own campaign spent less than $20,000, barely a blip. Mr. Romney spent little in Mississippi, while the super PAC supporting him spent almost $1 million.

Mr. Friess, who has been the principal donor to the Red White and Blue Fund, said on Tuesday that he had not ruled out giving more, but that he did not believe it would be necessary.

"My assessment is that the role I needed to play is maybe accomplished," Mr. Friess said. "I put