(Image Credit: Pete Souza/White House via Getty Images)

President Obama has spent more time raising money than any of his predecessors in recent history, crisscrossing the country on Air Force One to 175 re-election fundraisers so far in his first term.

His campaign, the Democratic National Committee and their joint accounts reported more than $173 million cash on hand at the end of May, $61 million more than rival Mitt Romney and Republicans.

And after smashing fundraising records in 2008, tapping $746 million from a historic donor roll of 3 million names, Team Obama has appeared on pace to do it again.

Still, Obama and Democrats are sounding the alarm for what would seem to be unthinkable: that they are poised to be outraised and outspent by Romney, the GOP and allied outside groups.

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"We see where we stand, and right now on a month-to-month basis, we've fallen behind," Obama told a group of high-dollar donors Friday on an 18-minute conference call from Air Force One, according to The Daily Beast, which obtained audio of the call from a participant.

"We just can't be outspent 10 to 1," Obama said. "That's what happened in Wisconsin recently. The Koch brothers and their allies spent more than the other side's entire campaign, our side's entire campaign.

"We are going to see more money spent on negative ads through these super PACs and anonymous outside groups than ever before. And if things continue as they have so far, I'll be the first sitting president in modern history to be outspent in his re-election campaign."

An Obama campaign official confirmed the veracity of the recording to ABC News, describing the meeting as a "routine finance call." (Obama uses a non-taxpayer-funded phone for political calls from the plane, the official said.)

Obama's message - that he could be the first incumbent U.S. president outspent - seeks to instill a sense of urgency in supporters as the campaign heads into a crucial stretch before the fall conventions. It also comes as part of an aggressive public and private fundraising drive that has sharply escalated in the past few weeks.

In the 48 hours before Saturday's June 30 monthly fundraising deadline, the Obama campaign sent out an unusual five email blasts pleading for cash; the appeals coming from Vice President Joe Biden, First lady Michelle Obama, DNC chairwoman Debbie Wasserman Schultz of Florida and the president himself.

"We might not out-raise Mitt Romney," Obama wrote Saturday morning in an email with the subject line "This is important." "But I am determined to keep the margin close enough that we can win this election the right way."

Obama has also significantly stepped up his fundraising activities on the trail, attending 33 money events in 30 days in June, triple the number he held in May and his biggest month of the year.

"We don't have to match these guys dollar for dollar because we've got a better grassroots operation and we've got a better message," Obama said on the Air Force One call. "The American people, the nice thing is they agree with our message when they hear it. We just can't be drowned out."

Obama's campaign advisers have estimated that Romney and pro-Republican outside groups, including nonprofit advocacy organizations and super PACs, will spent more than $1.2 billion to try to defeat Obama.

Democratic outside groups, including pro-Obama super PAC Priorities USA Action, have so far not shown the ability to keep pace with the other side.

The Romney campaign is expected to report raising more than $100 million in June. Obama campaign officials said they don't expect the president to match that number, but declined to offer specifics on their monthly haul.