Cumming, Georgia, Feb 20: Republican presidential contender Rick Santorum accused President Barack Obama of advocating a "world view" that is different from that of most Americans as he accused the Democratic incumbent of promoting the ideas of "radical environmentalists" and encouraging more abortions by requiring insurers to pay for prenatal tests.

Obama's campaign in turn Sunday criticized the former Pennsylvania senator for unfairly attacking the president's faith as the Republican nominating contest has pivoted from emphasizing the economy to social issues.

Santorum, a staunch opponent of abortion and gay rights, has surged past Mitt Romney in recent opinion polls of Republican voters after winning contests in Minnesota, Colorado and Missouri on Feb. 7.

Several polls have shown Santorum leading in Romney's native state of Michigan, where his father served as governor.

The primaries in Michigan and Arizona on Feb. 28 mark the end of a lull in the state-by-state contests to choose delegates to the party's national convention in late August in Tampa, Florida.

Though Santorum has climbed in the polls, Romney is considered the Republican front-runner nationwide, with more delegates from state-by-state voting that are necessary to claim the party's nomination.

The multimillionaire former private equity firm CEO also has far more money and a much stronger campaign organization than Santorum.

The two other rivals for the Republican Party nomination are former speaker of the U.S. House of Representatives Newt Gingrich and the libertarian-leaning Texas Rep. Ron Paul.

Meanwhile, Obama has seen his ratings in the polls steadily rising as the economy — by far his biggest weakness — continues to show signs of a recovery.

Santorum's attacks on Obama reflect an effort to position himself as the leading conservative alternative to Romney by appealing to the large bloc of religious voters and supporters of the small government, anti-tax tea party movement.

Romney, a former Massachusetts governor, has struggled to win over the party's conservative base which is wary of his shifting positions on sensitive issues like abortion and health care reform.

A day after telling an Ohio audience that Obama's agenda is based on "some phony theology, not a theology based on the Bible," Santorum on Sunday said he wasn't criticizing the president's Christianity.

"I've repeatedly said I don't question the president's faith. I've repeatedly said that I believe the president's Christian," Santorum told CBS television's "Face the Nation."

"I am talking about his world view, and the way he approaches problems in this country. I think they're different than how most people do in America," he said in the broadcast interview.

Santorum said Obama's environmental policies promote ideas of "radical environmentalists," who, Santorum argues, oppose greater use of the country's natural resources because they believe "man is here to serve the Earth."

He said that was the reference he was making Saturday in his Ohio campaign appearance when he denounced a "phony theology."

When pressed by reporters after he made the initial remark Saturday, however, Santorum made no mention of the president's environmental policies. Instead, he suggested that Obama practices one of the "different stripes of Christianity."

Santorum walked back those comments on CBS Sunday morning.

But later in the day, he again criticized Obama's "theology" — with no reference to his environmental policies — while speaking to more than 2,000 supporters gathered at a suburban Atlanta megachurch.

The president is "trampling on a constitutional right," Santorum said of the Obama administration's recent decision to allow employees of religious schools and hospitals to have birth control covered by their insurance policies.

"It is imposing his ideology on a group of people expressing their theology, their moral code," Santorum told those gathered in the First Redeemer Church.

Obama's campaign said Santorum's initial remarks Saturday about the president's "phony theology" were another attack on his faith by Republican rivals in a nominating contest that has grown increasingly bitter and negative.

"It's just time to get rid of this mindset in our politics that, if we disagree, we have to question character and faith," said Robert Gibbs, Obama's former White House press secretary, Sunday on ABC's "This Week."

"Those days have long passed in our politics. Our problems and our challenges are far too great," Gibbs said.

Questions about whether Santorum can sustain his rise in the polls come amid new scrutiny of his views on social issues. In recent days, Obama's campaign team has shifted gears to consider the possibility that Santorum rather than Romney will emerge as his opponent for the November election.

Campaign officials confirm that Obama's Chicago-based organization has begun combing through Santorum's background looking for possible lines of attack.

It also emailed Obama's Pennsylvania supporters this past week asking for material that could be used against Santorum in upcoming speeches and ads.

Obama's Pennsylvania campaign director, Bill Hyers, said in an email to supporters that Santorum's "extreme-right social views are as out of touch as they are memorable."

Santorum said his claim that Obama's health care overhaul encourages abortions stems from the requirement for insurance companies to pay for prenatal testing, which he said will result in more pregnant women having more procedures. He specified amniocentesis, a procedure that can identify physical problems in the unborn.

"The bottom line is a lot of prenatal tests are done to identify deformities in utero and the customary procedure is to encourage abortion," he said.

A doctor recommended abortion when a sonogram discovered health problems for Santorum's youngest daughter, who was born three years ago with a genetic condition known as Trisomy 18, which typically proves fatal. She has lived longer than most children born with the condition.

"This is typical," Santorum said. "This is what goes on in medical rooms around the country."

He said he's critical of the mandate in Obama's health care plan that insurers must pay for the tests, not of prenatal testing in general.

Gingrich is trying to make yet another comeback in the race on March 6, or Super Tuesday, when 10 states hold nominating contests, including several southern states which he considers friendly terrain.

Gingrich insisted on "Fox News Sunday" that the Republican presidential candidates must win their home-turf contests or face serious questions about continuing in the race, attempting to raise the stakes for Romney in Michigan.

Gingrich also acknowledged that he must win the March 6 vote in Georgia, a state that launched his political career when it sent him to the House of Representatives more than 30 years ago. The same, he said, goes for Santorum during the April primary in Pennsylvania.

"If any of the three loses our home state ... you have, I think, very, very badly weakened candidacies," Gingrich said.