As his campaign surges, Rick Santorum is testing an untested model for incorporating religion into his message. He is betting that Americans want a president who uses faith not just to inspire — but also to judge.

This weekend, Santorum told supporters in Ohio that President Obama’s environmental views reflect “some phony theology. Not a theology based on the Bible.” Santorum said later that he believes Obama is a Christian, but he says that the president subscribes to the idea that the Earth’s needs should be put above mankind’s.

“I don’t believe . . . that’s what we’re here to do,” Santorum said on CBS’s “Face the Nation” on Sunday. “We’re not here to serve the Earth. The Earth is not the objective. Man is the objective.”

That argument seems to fit an older pattern in Santorum’s rhetoric. As a columnist for the Philadelphia Inquirer, Santorum blasted other politicians and Catholic universities for disregarding church doctrine.

The usual rules for talking about faith on the campaign trail call for candidates to speak about their religion in uplifting, accessible generalities. Now, Santorum seems to have cast himself as a candidate bold enough to tell others where they’re wrong.

“He has this internal tic, of wanting to get into what I call theological disputation. And theological disputation is a loser,” said Jacques Berlinerblau, a professor at Georgetown University who has studied the use of religion in U.S. politics. He meant that Santorum seeks to tell others how to behave and even what to believe, using his own specific beliefs as an unshakable guide.

Berlinerblau said the danger, even among other Catholics, was that Santorum would seem gratingly familiar. “They know Rick Santorums. They’ve met Rick Santorums their whole life,” he said. “It’s just, ‘Well, I know what that guy’s about, and I don’t want anything to do with it.’ ”

In an interview Sunday, a spokesman for Santorum’s campaign said the candidate was not judging Obama’s private religious beliefs. But, spokesman Hogan Gidley said, “theology” was still the right word for what Obama had wrong.

“Theology’s a worldview. And Obama sees the world differently. I mean, someone who apologizes for America’s greatness, and someone who thinks the government knows best on health care, I mean those are different theologies,” Gidley said. “Rick is separating the two. One’s own personal religious beliefs are different than a worldview or a theology as it relates to governing and the government.”

During the campaign, Santorum has focused extensively on three issues where his views align with Catholic bishops. He opposes abortion and same-sex marriage, and he fought against a government mandate for religiously affiliated institutions to provide contraceptive coverage in their health insurance.

In past campaigns, many candidates have limited themselves to broad statements about their belief in God, and their confidence that He has blessed America specially. The only Catholic president, John F. Kennedy, said on the campaign trail that “I believe in an America that is officially neither Catholic, Protestant nor Jewish.”

In this campaign, former Massachusetts governor Mitt Romney, a Mormon, has stayed closer to the traditional model with his brief invocations of “my faith.”

But in Ohio this week, one Republican delegate said Santorum was right to make his own religion — and Obama’s — an issue in this campaign.

“He’s stating the obvious,” said Bryan Williams, 47, who works for a trade group of builders and contractors, contending that Obama “is largely a secular person.”

Williams said he took Obama at his word that he is a Christian but said that it’s fair game for a candidate’s religious beliefs to be considered in a campaign.

“The public needs to know how you’re anchored,” he said.

In Michigan, which holds its primary Feb. 28, a recent Detroit News poll showed Santorum leading Romney, 34 percent to 30. Still, there is a potential downside to a message so confidently rooted in religious belief — and so frank about others’ mistakes.

“Scolding just makes you look old. I shouldn’t say old, so I’ll say something else: Scolding just makes you look dour,” said Anthea Butler, a professor of religious studies at the University of Pennsylvania. “You need to be a little bit more” than that, she said.

Santorum’s comment about Obama’s “theology” echoes themes he wrote about as a columnist for the Philadelphia Inquirer. He began writing the columns — most of which are not available online — after an 18-point electoral loss in 2006. The loss came in a Democratic year, but it was also blamed partly on Santorum’s stances on social issues: In a 2005 book, he wrote: “For some parents, the purported need to provide things for their children simply provides a convenient rationalization for pursuing a gratifying career outside the home.” And Santorum had compared homosexual sex acts to adultery, polygamy and incest.

In one of these columns, Santorum was critical of Catholic colleges: “You might be surprised to learn that most professors are not Catholic and that the Catholics are often nonpracticing.” Even the University of Notre Dame, he said, had hosted performances of “The Vagina Monologues.”

And Santorum wrote about two Democratic politicians — then-House Speaker Nancy Pelosi (Calif.) and then-Rep. Patrick Kennedy (R.I.) — who he said had been scolded by the church for not following Catholic teaching on abortion.

He applauded Pope Benedict XVI for taking issue with Pelosi’s views in a personal meeting, and for not allowing Pelosi to be photographed with him: “Dissenting Catholic politicians who deliberately mislead others about the church’s core teachings will not be given another chance to do so by having their picture taken with the vicar of Christ.”

“Catholics must be true to their consciences. But that is not a free-floating guide that we can define ourselves,” Santorum wrote in August 2008, when a Catholic bishop had called out Kennedy over abortion. “A Catholic is required to form his conscience in accordance with the church’s teachings on faith and reason.”

Sonmez reported from Akron, Ohio.