WASHINGTON — The Democratic presidential nominee, Senator Obama, raised $66 million in August, a record for a presidential candidate that illustrated his continuing appeal to donors and his robust outreach to new contributors.

The campaign said it raised the money with the help of more than a half million, first-time donors. By comparison, the Republican presidential nominee, Senator McCain, raised $47 million in August, a personal best for his campaign as well. The monthly figures for both candidates were especially noteworthy because August is typically a slow month for fundraising.

Mr. Obama’s totals, however, also underscore the challenge he faces in the remaining two months of the campaign. Mr. McCain, for now, has a significant advantage because he has accepted $84 million in taxpayer funds under a public financing system that Mr. Obama chose to bypass in favor of raising more money.

The combined efforts of the two campaigns and the two national parties left both candidates on nearly equal financial footing with about $94 million at the end of August, according to campaign and party officials who discussed the finances on Sunday.

Mr. Obama had $77 million in the bank at month’s end, and the Democratic National Committee had $17.5 million.

Mr. McCain ended the month with about $18 million in cash, which he had to transfer to the Republican National Committee because of his decision to participate in the public finance system. The party committee had $76 million in the bank before the transfer. A party official said the party also had about $20 million in a joint fundraising committee and in special state party accounts that can be used to help Mr. McCain.

But Mr. McCain has a head start over Mr. Obama with the $84 million in federal funds. By accepting that money, however, he can no longer raise money for his campaign from donors and is limited to spending only that amount. As a result, any additional fundraising can only be done for the GOP.

Democratic fundraisers say Mr. Obama and the Democratic Party must do even better than their August totals to stay ahead of Mr. McCain and the well-heeled RNC. Mr. Obama and the DNC raised a combined total of more than $83 million, but fundraisers say their joint totals ahead should exceed $100 million a month.

Mr. McCain and the GOP have been able to stay essentially even with Mr. Obama and the Democrats through August because the RNC has had strong fundraising and low spending. The Democratic National Committee has had lower fundraising and higher spending.

In August, the RNC raised about $22 million, shy of its $26 million sum in July. The Democratic National committee reported raising $17.3 million in August, short of the $20 million raised in July.

Even though he can raise no more money for his campaign, Mr. McCain has placed his popular running mate, Governor Palin of Alaska, on an aggressive fundraising schedule for the Republican Party. She has about one fundraiser every two days for the remainder of the campaign.

Mr. Obama has scheduled a series of fundraisers and has continued to make Internet and e-mail appeals his donors and supporters. The campaign reported that it raised $10 million in less than 24 hours this month, following Palin’s address to the Republican National Convention.

Overall, Mr. Obama has raised more than $440 million for his presidential campaign, an unprecedented amount. The campaign said it has more than 2.5 million donors. Mr. McCain has raised $194 million.

“The 500,000 new donors to the Obama campaign demonstrate just how strongly the American people are looking to kick the special interests out and change Washington,” his campaign manager, David Plouffe, said in a statement.

A McCain campaign spokesman, Tucker Bounds, said the announcement provides “66 million reminders that Barack Obama is willing to stray from reform, break his word to the American people and forgo public financing in favor of his own ambitions. Americans need change, not self-promotion.”

Mr. McCain’s campaign reported raising $10 million in the final days in August, a surge the campaign has attributed to Ms. Palin’s selection as running mate.