WASHINGTON — President Barack Obama has spent more campaign cash more quickly than any incumbent in recent history, betting that heavy early investments in personnel, field offices and a high-tech campaign infrastructure will propel him to victory in November.

Since the beginning of last year, Obama and the Democrats have burned through millions of dollars to find and register voters. They have spent almost $50 million subsidizing Democratic state parties to hire workers, pay for cellphones, and update voter lists. They have spent tens of millions of dollars on polling, online advertising and software development to turn Obama’s fallow volunteers corps into a grass-roots army.

The price tag: about $400 million from the beginning of last year to June 30 this year, according to a New York Times analysis of Federal Election Commission records, including $86 million on advertising.

But now Obama’s big-dollar bet is being tested. With less than a month to go before the national party conventions begin, the president’s once commanding cash advantage has evaporated, leaving Mitt Romney and the Republican National Committee with more cash on hand than the Democrats at the beginning of July.

Despite Obama’s multimillion-dollar advertising barrage against Romney, he is now being outspent on the airwaves with Romney benefiting from a deluge of spending by conservative super PACs and outside groups. While Romney has depleted much of his funds from the nominating contest, he is four weeks away from being able to tap into tens of millions of dollars in general election money. And many polls show the race to be very close.

Obama’s cash needs – he spent $70.8 million in June alone, more than half on advertising and far more than he raised – has brought new urgency to his campaign’s fundraising efforts. His advisers have had to schedule more fundraising trips than originally planned to big-money states like New York, according to donors involved in the effort. The super PAC supporting his campaign, Priorities USA Action, is enlisting former President Bill Clinton as a rainmaker, hoping to counter conservative groups.

Spending stirs worries

Obama’s heavy expenditures – and his campaign’s pressure on bundlers to find and groom new donors – have stirred worries among other Democrats, who have long taken Obama’s financial supremacy for granted.

“There is a lot of worry that Romney’s folks are raising so much more,” said one of Obama’s top fundraisers, who was granted anonymity to discuss private conversations with the campaign. “I just don’t think there’s a lot of high-dollar money left on the table.”

But in interviews, party and campaign officials defended the approach of spending money to build out the campaign, saying they believed that the wisdom of Obama’s strategy would be demonstrated at the voting booth in November.

“The earlier the better,” said Adam Fetcher, an Obama campaign spokesman. “Starting a conversation with a persuadable voter months before Election Day allows us to be more effective in responding to that voter’s priorities than if they first hear from us a few weeks out. Building and maintaining our grass-roots foundation takes time and resources, but we believe those early investments will make a difference.”

Voter registration investment

Mindful that the recession has displaced many people who voted for Obama in 2008, especially those with low incomes, the campaign has also invested heavily in voter registration. That has paid dividends in states like Nevada, where Democrats have steadily expanded their registration advantage over Republicans in recent months. In Ohio, the early deployment of money and a field staff last year also allowed the campaign to help Democrats fight a Republican-led effort to restrict early voting in the state.

“You can pay for direct mail or TV ads at the last minute, but you can’t shortcut long-term volunteer training programs,” said the official, who was granted anonymity to discuss the campaign’s spending strategy. “The relationships we’ve built, the depth of what people know about their communities, our data systems, the training and organization – good luck doing that in less than 100 days.”

Kitty Bennett and Derek Willis of the New York Times contributed.