Romney appeared Saturday with televangelist Pat Robertson in the key swing state of Virginia, and seized upon the row at last week's Democratic convention sparked when delegates removed language about God from their platform.
After reciting the Pledge of Allegiance, Romney told the crowd: "I will not take God out of... our platform. I will not take God out of my heart. We are a nation that's bestowed by God."
Romney said Americans needed a new president who will "commit to a nation under God that recognizes that we, the American people, were given our rights not by government but by God himself."
The former Massachusetts governor also appeared to imply that Democrats wanted to remove the phrase "In God We Trust" from US currency.
The Obama campaign swiftly responded to Romney's rhetoric, describing it as a "Hail Mary" pass -- a desperate long throw in the dying moments of an American football game when defeat is nigh.
Spokeswoman Lis Smith accused the Republican nominee of launching "extreme and untrue attacks against the president and associating with some of the most strident and divisive voices in the Republican Party."
"This isn't a recipe for making America stronger, it's a recipe for division and taking us backward," Smith said.
The Romney team shot back that it was Obama's campaign, not Romney's "that pits people against each other."
"It's just so far from what he promised voters when he was a candidate," campaign adviser Kevin Madden told AFP.
The new ripple in the campaign comes amid signs of a polling bounce for Obama out of his convention last week, as he climbed a point into a 49-45 percent lead over Romney in Gallup's daily tracking poll.
His approval rating as measured by Gallup held steady at 52 percent, its highest mark since he ordered the operation to kill Al-Qaeda leader Osama bin Laden in May 2011.
Romney enjoyed no discernible benefit in the polls from his convention.
Robertson, who met with Romney before the Republican nominee addressed about 3,000 people at a military aviation museum in Virginia Beach, has a history of inflammatory rhetoric.
He said Haiti was struck by a devastating earthquake in 2010 because the impoverished and frequently disaster-struck nation was cursed after making a deal with the devil.
Last week, Obama was forced to order Democrats to restore a reference to America as a land of "God-given" potential to their platform -- the list of issues to which the party is committed.
Republican campaigns have frequently used religious and cultural issues to drive up turnout in close elections, and now as a veiled attack on Obama, who has frequently felt compelled to point out that he is a practicing Christian.
With both candidates seeing the votes of white, working-class voters in battleground states as critical, cultural and religious issues could take on added importance ahead of the November 6 election.
Obama turned his attention to the swing voter belt of central Florida, which usually decides the destiny of the state, and sometimes the presidency.
"The values we are fighting for are not Democratic values, they are not Republican values, they are American values," Obama said, as his campaign flexed organizational muscle and turned out 11,000 people.
Obama was introduced in St Petersburg, Florida, by Charlie Crist, the former Republican governor of the Sunshine State, who says he was driven from his party after losing a Senate primary to Tea Party-backed Marco Rubio in 2010.
"We have a leader with a cool head, his name is President Barack Obama," said Crist, who is popular among moderates in Florida and seen as a possible candidate for statewide office as a Democrat.
The president renewed his attack on Romney over what he calls "trickle-down" Republican economics that have demonstrably failed and would risk igniting a new financial crisis.
"Tax cuts, tax cuts, gut a few regulations," Obama said in characterizing Romney's agenda.
"More tax cuts, tax cuts when times are good, tax cuts when times are bad. Tax cuts to lose a few extra pounds, tax cuts to improve your love life."
Romney's planned return to a NASCAR racetrack, however, was a washout due to heavy rain, denying the Republican presidential nominee the opportunity to announce: "Drivers, start your engines!"
The Federated Auto Parts 400 race at Virginia's Richmond International Raceway was delayed for several hours.
Romney's planned trip was a bald play at the NASCAR vote, as he seeks to increase his popularity among white males, the demographic he needs to win in order to counter Obama's handy lead among women, blacks and Hispanics.
