President Obama has fallen behind Republican Mitt Romney in monthly fundraising totals and may now be the underdog in the 2012 money race, given the juggernaut he faces of conservative groups with unlimited contributions at their disposal.

The trend has set off at least a mild sense of panic in the Obama campaign, which warned donors on Monday: “We will get beat if this continues.”

The Romney campaign announced Monday that it raised an eye-popping $106 million last month in conjunction with the Republican National Committee, compared with just $71 million announced by Obama and the Democratic National Committee. The gap, at $35 million, is wider than it was in May, when Romney and his party allies raised $17 million more than the Democratic side.

The momentum shift marks a change in fortunes for Obama, whose 2008 victory was propelled by a breathtaking fundraising operation that brought in $745 million by Election Day, much of it fueled by grass-roots donations. In September 2008 alone, Obama and the DNC brought in $193 million.

The roles appear to be reversed this time, as Obama’s cash advantage over Romney rapidly deteriorates because of blockbuster fundraising by Republicans. The Obama campaign also faces a tide of spending by pro-Republican advocacy groups that can raise unlimited funds from wealthy individuals and corporations.

Romney raised more than Obama in May, the first full month of joint fundraising between the presumptive GOP nominee and the RNC. (The Washington Post/Source: The campaigns)

The worry among the president’s team was palpable.

“We had our best fundraising month yet, and we still fell about $35 million short,” Ann Marie Ha­ber­shaw, the Obama campaign’s chief operating officer, wrote in a fundraising plea to supporters. “We can win while being outspent — but we need to keep it close.”

Romney has relied more than Obama on wealthy contributors who are able to give maximum contributions under federal rules.

His schedule has been heavily dominated by high-dollar fundraising events, such as a June retreat in Park City, Utah, and a swing through the Hamptons this past weekend.

The bulk of Romney’s June total — $70 million — was taken in by a joint victory fund that can accept as much as $70,800 per donor. The campaign itself raised $24 million, while another $12 million came into the RNC, officials said.

“May was already a turning point, and I think June was a turning point plus,” said Bobbie Kilberg, a top Romney fundraiser in Virginia. “You feel an extraordinary momentum and excitement that I have not seen in all the fundraising efforts I have been involved with on the Republican side. It shows a very strong belief in Mitt’s chances of winning the presidency.”

Daniel Dumezich, a fundraising co-chair for Romney in Indiana, said he was “surprised at the total domination of the Obama team” in June and predicted it would continue.

“People understand that the path that President Obama is taking us on is one of socialism,” Dumezich said. “If he keeps advancing the causes of illegal aliens and those kinds of issues, then I think, yes, Governor Romney will keep raising more money.”

Obama campaign manager Jim Messina and other Democrats have been fretting all year about the chance of being outspent by Republicans, but the concerns have come to a boil in recent weeks.

Conference calls with Obama’s national finance committee have taken on an increasingly worried tone, said Andy Spahn, an entertainment industry executive who has raised more than $500,000 for Obama’s campaign.

“Given these reports it’s clear that we’re going to need an even more aggressive fundraising push,” Spahn said. “There’s real concern about the unregulated Citizens United money, so to speak.”

Despite the trends, Obama has raised more than Romney over the full 2012 election season, allowing the incumbent to invest tens of millions of dollars in offices in all 50 states. Romney and the RNC said they had $160 million in cash on hand at the end of June; the Obama campaign, which had a similar amount with the DNC at the end of May, declined to release its cash figure for June. Official reports are due to the Federal Election Commission on July 20.

Anthony Corrado, a campaign-finance expert at Colby College in Waterville, Maine, said the 2012 race is in some respects similar to 2004, when Democrats posted strong fundraising numbers motivated by opposition to George W. Bush.

The Democratic nominee that year, Sen. John F. Kerry (D-Mass.), outraised Bush 2 to 1 during the period between locking up the nomination and the party conventions, Corrado said.

Kerry’s bid that year was also aided by a constellation of liberal groups raising unlimited funds.

One major difference in 2004 was public financing, which helped even the playing field in the final weeks of the campaign.

Neither Obama nor Romney plans to claim public matching funds, which could allow money advantages that emerge this summer to persist through Election Day.

“What we’re seeing this year is many of the same dynamics at play. It’s just that the motivation to give is stronger on the Republican side,” Corrado said. “I don’t know if this is a turning point, but I think it shows we’re going to see very strong Republican fundraising going forward.”