Compared with Mr. Obama, Mr. McCain drew a slightly larger percentage of his big-donor money from the financial industry, about a fifth of his total. The next biggest amount in large checks for Mr. McCain came from real estate and then donors who identified themselves as retired. With his emphasis on offshore drilling, Mr. McCain has also enjoyed heavy support from generous benefactors in the oil and gas industry, a group Mr. Obama drew relatively little from.

After the financial arena, Mr. Obama drew the most in checks of $25,000 or more from retirees and lawyers  Mr. McCain collected significantly less in large donations from lawyers  followed by those in real estate.

Mr. Obama also drew a significant amount from big givers in the entertainment industry, who contributed relatively little to Mr. McCain. In contrast, donations from the private equity and hedge fund industries accounted for a significantly greater amount of the giving from Mr. McCain’s largest donors, compared with Mr. Obama’s.

Certain companies were especially generous to a particular candidate. Three top executives of Merrill Lynch, for example, wrote checks of $28,500 each to Mr. McCain; among them was the chief executive, John A. Thain. A dozen employees at Goldman Sachs wrote checks of $25,000 or more to Mr. Obama.

Donations to these joint fund-raising committees have surged this election cycle, taking in nearly $300 million this year through September  with Mr. McCain collecting slightly more than Mr. Obama  compared with $69 million in 2004. Campaign finance watchdogs call it a worrisome trend, saying the heavy emphasis on such arrangements brings candidates one step further into the embrace of major donors.

“This is subverting the whole notion of candidate contribution limits,” said Steve Weissman, associate director for policy at the Campaign Finance Institute.

Individuals are normally limited to contributing $2,300 to presidential candidates for the primary and another $2,300 for the general election. But the joint fund-raising committees allow donors to enjoy the clout that comes with writing a single large check that can cover the maximum contributions to the candidates, as well as $28,500 to the national party. In Mr. McCain’s case, that check could also include $10,000 apiece for several state parties and $2,300 to a legal compliance fund for the general election. The money directed to the national and state parties can then be used to help the candidates under certain restrictions.