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As debate over religion and social policy at least temporarily steals the spotlight in the presidential race, the Obama campaign today took aim at the tax and budget plans of Republican frontrunners Mitt Romney and Rick Santorum, claiming neither will trim the deficit as promised if they win the White House.

"We've heard a lot of unfounded claims during the Republican primary and a lot of unrealistic promises that would be very difficult for a lot of these candidates to keep as president," Obama campaign spokesman Ben LaBolt told reporters on a conference call. "But Gov. Romney and Sen. Santorum's claims about the deficit are among the hardest to square because they're easiest to debunk."

In a memo released this morning, the campaign provided an analysis of how the candidates' math allegedly does not add up.

Obama aides, citing studies from the Tax Policy Center and Center on Budget and Policy Priorities, conclude Romney's public budget proposals would add $175 billion a year to the deficit.  They claim his proposed tax cuts and increased defense spending would not be adequately offset by as yet unspecified spending cuts the size of which are deemed "simply not plausible."

The memo also claims Santorum's plan would add $990 billion to the deficit in 2015.

The baseline for the analysis, officials said, was the latest Congressional Budget Office projection of deficits of 5 percent of GDP (or $981 billion) in 2016 - the end of the next presidential term - if current policies including the Bush tax cuts are extended.

Romney has claimed he'd cut $500 billion from the budget by 2016, while Santorum envisions $5 trillion in cuts to government spending over five years.

"I have been involved in economic policy for four presidential election cycles. The Romney and Santorum plans are by far the most unrealistic budget plans I have ever seen," said Jeff Liebman, an economist, former deputy director of the Office of Management and Budget, and professor of public policy at Harvard University. "Their budget math simply doesn't add up."

Romney campaign spokeswoman Andrea Saul did not directly refute the Obama campaign's analysis when asked about it by ABC News. She instead pointed to the more than $5 trillion in deficits accrued during Obama's term.

"President Obama is in no position to criticize Mitt Romney's proposals to cut taxes and restore fiscal responsibility," Saul said in an email. "After all, this is the President who just proposed the largest tax increase in American history and has given us four straight trillion-dollar budget deficits.  Middle-income Americans have been crushed by the Obama economy and millions of American workers have just given up looking for work.  This was the president who told us that if he didn't fix the economy in three years, he'd be looking at a one term proposition.  It's time to collect."

Obama's 2013 budget is projected to reduce the deficit by $4 trillion over the next 10 years.

The targeting of Santorum is the latest sign the Obama campaign is broadening its focus on potential Republican general election challengers after spending months focusing near-exclusively on Romney.

"As Sen. Santorum has risen in the polls, the scrutiny of his policies will follow," said LaBolt. "While both Gov. Romney and Sen. Santorum both claim to be budget-cutters, they've both introduced proposals that would lead to massive increases in the deficit. So we thought it was appropriate to raise those questions today."