White House hopeful Rick Santorum rowed back Sunday from a brazen attack on Barack Obama's faith, reframing his earlier remarks as a criticism of the president's radical "world view."

Santorum, a former Pennsylvania senator who has joined Mitt Romney at the front of the Republican pack seeking to take on Obama in November, is a staunch Catholic and a fierce opponent of gay marriage and abortion.

Obama, a Christian who attends church regularly with his family, has suffered slurs in the past from opponents who would paint him as un-American and even a Muslim -- his middle name is Hussein.

At a campaign stop in Ohio on Saturday, Santorum accused Obama of believing in "some phony ideal, some phony theology. Not a theology based on the Bible."

His remarks came after Republicans escalated election-year attacks on the president in a feud over health insurance coverage of birth control, accusing him of a "systematic" assault on religion.

The assault seems designed to make Obama and his Democratic allies pay a political price -- notably among Catholic swing voters in battleground states vital to his reelection in November.

Santorum's remarks appeared to go a little beyond the pale, though, and on Sunday he moved to water them down, telling CBS he had actually been referring to the president's views on energy and the environment.

"I wasn't suggesting the president's not a Christian. I accept the fact that the president is a Christian," he said.

"It's not questioning the president's beliefs in Christianity. I'm talking about the belief that man is -- should be in charge of the Earth and have dominion over it and be good stewards of it."

Santorum suggested Obama's "world view" elevated the Earth above man and accused the president of politicizing the global warming debate with unproven science "to centralize power and to give more power to the government."

"I was talking about the radical environmentalist," he said.

"That's what I was talking about -- energy: this idea that man is here to serve the Earth, as opposed to husband its resources and be good stewards of the Earth. And I think that is a phony ideal."

Robert Gibbs, a top Obama campaign adviser who was formerly his White House spokesman, said Santorum's comments were reflective of a "race to the bottom" in the Republican party's recent political discourse.

"I think this (Republican) primary... has been a race to the bottom. We have seen nastiness, divisiveness, ugliness, distortions of opponents' records, of the president's records," Gibbs told ABC television.

Republican contenders have taken frequent swipes at Obama's faith in a bid to court favor among the influential Tea Party group of conservatives and others on the far right of the party.

Santorum insisted his remarks on Saturday to a Tea Party gathering were not meant to reopen that recurring discussion.

"I've repeatedly said I don't question the president's faith. I've repeatedly said that I believe the president is a Christian. He says he is a Christian.

"But I am talking about his world view or his -- the way he approaches problems in this country. And I think they're different than how most people do in America."

In other remarks sure to prove controversial, Santorum told CBS on Sunday that amniocentesis "more often than not" results in abortion, explaining his opposition to routine screening procedures to assess the health of a fetus.

"People have a right to do it, but to have the government force people to provide it free just is a bit loaded," he said.

Santorum was responding to questions about comments he made the day before at a Christian Alliance luncheon in Ohio suggesting that the mandate in Obama's 2010 health care law was intended to increase abortions.