President Barack Obama left the White House Sunday. Getty Images

WASHINGTON—President Barack Obama's $181 million fundraising haul in September is helping to calm Democrats who fear a deluge of negative ads from Republican super PACs and remain anxious after Mitt Romney's strong performance in last week's presidential debate.

Mr. Obama's fundraising total last month, raised in conjunction with the Democratic National Committee, is larger than any candidate has reported in any month of the 2012 election. It will allow Mr. Obama to maintain a robust presence on the airwaves during the last month of the campaign.

Mr. Romney's campaign hasn't yet released its September fundraising total. In August, the Obama campaign and its affiliates took in $114 million, while the Romney campaign and affiliated party committees collected $111 million. Those were monthly records for each campaign.

Mr. Obama's campaign and its party affiliates have outraised Mr. Romney's—taking in $742 million through August, compared with $638 million by Mr. Romney and GOP party committees. But super PACs backing Mr. Obama have raised far less than their GOP opponents, though Democrats also benefit from the support of organized labor.

Dick Harpootlian, a member of Obama campaign's national finance committee and chairman of the South Carolina Democratic Party, said the September fundraising total shows the president can approximate parity with Mr. Romney's campaign and its allies.

"That's an extraordinary number for September, far higher than anyone anticipated," Mr. Harpootlian said. "What's happening is the small donor base is coming home in a big way."

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"The jobs numbers and the campaign-finance numbers will take Democrats out of group therapy and keep them focused on the urgent task ahead of re-electing the president," said Robert Zimmerman, an Obama fundraiser based in New York. He was referring to a government report Friday that said the unemployment rate fell to 7.8% in September, the lowest rate since January 2009.

Mr. Romney's campaign says the GOP candidate's strong performance in last week's debate has spurred new donors, and that the campaign raised $12 million in the two days following the debate.

Mr. Obama and his allies have run more TV ads in some battleground states than Mr. Romney and his supporters. That is in part because he has been better able than his Republican rival to take advantage of low ad rates that under law must be offered to candidates but not to outside groups and political parties.

Mr. Obama, the Democratic National Committee and another party committee had $125 million in the bank at the end of August, mostly in the account of Mr. Obama's own campaign. Some $7.1 million of the total was controlled by the Democratic National Committee, which has less access to low TV ad rates than does the Obama campaign.

By contrast, a larger share of Mr. Romney's money was held by the Republican National Committee. Mr. Romney and affiliated party committees had $170 million at the end of August. Of that, about $75 million had been raised by the Republican National Committee.

The difference becomes meaningful when the two sides buy ads. For example, the Republican National Committee once paid $6,500 to run a spot during "Dancing with the Stars" on the ABC affiliate in Cincinnati, while Mr. Obama paid just $2,000 an ad for the same time, according to records maintained by the Federal Communications Commission.

American Crossroads, a Republican super PAC, paid $700 to run an ad during NBC's "Today Show" in Orlando last week, while Mr. Obama paid $600.

That helps account for why Mr. Obama and his allies have run more TV ads in some battleground states than have Mr. Romney and his allies.

Mr. Obama's campaign, which is paying for the vast majority of Democratic advertising this election, and Democratic super PACs and other allies spent $45 million on ads during the last three weeks of September, according to a Wesleyan Media Project analysis of data from Kantar Media/CMAG. That bought Democrats more than 93,000 TV spots.

Mr. Romney and his allies, including super PACs and party committees, spent only slightly less money—about $43 million—but that sum purchased 69,000 spots.

—Brody Mullins contributed to this article.

Write to Danny Yadron at and Peter Nicholas at