Jae C. Hong, Associated Press
Democratic presidential candidate Sen. Barack Obama, D-Ill., speaks at a fundraiser in New York on July 9. Obama swamped John McCain in June fundraising and now has pulled in an eye-popping $340 million.

WASHINGTON — Though he's raking in the cash so far, Barack Obama's decision to forgo public funds for the fall campaign means he must keep up his torrid pace — a tall order that will tax his time, test his Internet support and require the help of Democratic donors who once wished for his defeat.

The Democratic nominee-in-waiting had his second-best fundraising month in June, a $52 million haul that swamped presidential rival John McCain by more than 2-1. He also got a big boost from his party, which raised nearly five times as much as it had in May.

The new figures underscore the Illinois senator's status as a fundraising star. He has raised $340 million during his presidential run to McCain's $132 million.

Obama's June total also reversed a three-month decline and helped close a cash-on-hand gap between the Democratic and Republican presidential operations. Together, Obama and the Democratic National Committee had $92 million in the bank at the end of June compared with $96 million for McCain and the Republican National Committee.

But the totals also set a tough new standard for Obama's presidential campaign: The $52 million he raised in June is now a baseline, not a high water mark.

"For him to maintain the pace that it looks as if he will need, he will have to match his best-ever month every month," said Michael Malbin, executive director of the Campaign Finance Institute, a nonpartisan group that tracks trends in political money. "That's what he's done this time, pretty close to his best-ever month, and he'll need to sustain this pace or increase it."

Obama's best fundraising month was February, when he took in $55 million.

Overall, the McCain campaign has estimated that it and Republican Party committees will have $400 million to spend on the presidential election in the months before the November election.

To surpass that level of spending, Obama and the Democratic Party will have to raise about $100 million a month.

That task is making some Democrats anxious.

"You don't want to be in a situation at the critical time in September and October when you have not met your budget expectations," said Hassan Nemazee, who was Hillary Rodham Clinton's national financial co-chair and is now raising money for Obama and the DNC. "You're going to find yourself between a rock and hard place in terms of meeting your numbers."

McCain plans to accept $84 million in public money in the fall — money he won't have to lift a finger to collect but which will limit his campaign's spending in the fall. The RNC and other party committees will foot the remainder of his campaign bills through coordinated and independent spending on his behalf.

Obama chose to become the first candidate in three decades to bypass the public funds — the money from checkoff boxes on taxpayers' returns — and that places a premium on his ability to raise more than McCain's $84 million.

"We have developed a strategy — a very aggressive strategy — that will only work if our millions of supporters continue to contribute their time and their money," Obama campaign manager David Plouffe said in an e-mail to donors Thursday.

Then there's Clinton, Obama's foe-turned-supporter.

How much the Obama campaign plans to rely on Clinton's former donors remains to be seen. Her fundraisers say it will be much easier for them to raise money for Obama if his donors contribute to Clinton to help reduce her vendor debts, which at the end of May stood at about $10 million and growing.

"The most readily available, identifiable pool of new people for the Obama campaign to access is unquestionably the Clinton donors," said Nemazee, who personally raised $400,000 for Obama and the DNC in a matter of days recently.

Tad Devine, a political strategist who was a senior adviser in Democrat John Kerry's 2004 presidential campaign, says Obama could overcome many financial obstacles by selecting Clinton as his running mate.

"If you're planning the first general election that is not going to be financed by public money and you have the potential to pick someone who has already demonstrated the capacity to raise in excess of $200 million, I would think that would be an enormously consequential consideration," he said.

Obama has maintained a busy fundraising schedule in July, holding at least one event a night as he campaigns in big-dollar locales such as Atlanta, Chicago, Washington and New York. Nevertheless, he is taking himself out of the fundraising circuit starting this week when he leaves for at least a week of foreign travel.

Both Obama and McCain have been helping raise money for their respective parties, as well. The DNC had raised only $4.7 million in May, but after Obama locked up the nomination the party raised $22.5 million. The RNC also is getting help from President Bush, who was scheduled to attend an RNC fundraiser in Napa, Calif., Thursday evening that was expected to raise $850,000.

Both campaigns are already spending their money. Obama has set up big field operations in several states, most recently in the new battleground of Virginia. The campaigns are also spending significantly on advertising — Obama about $7.6 million a week in 18 states and McCain and the RNC together some $7.3 million a week in 11 states.

Several Democratic fundraisers and strategists predicted money will come to Obama and the DNC in ever-increasing amounts. They say the Democratic National Convention in late August should serve as a springboard for record cash.

"I don't think summer fundraising at the end of a primary is a barometer for the potential fundraising in the general election," said Devine.

Obama has had extraordinary success tapping small donors through the Internet, particularly young people motivated to give for the first time. But he has caused some consternation recently among his core supporters for supporting an intelligence bill that many Democrats opposed and for other moves that appeared designed to attract more moderate independent voters.

It is significant that of the $52 million that Obama raised in June, only $2 million was for the general election. That means that he has been able to continue to tap new donors and donors who have yet to contribute the $2,300 maximum for the primary portion of his campaign. And he can go to them again for general election contributions.

Unlike McCain, Obama can roll over unused primary election money into the fall general election contest.