— Looking to court this state’s critical voting bloc of evangelical Christians, Republican presidential candidates sharply attacked secularism and the Supreme Court while calling for greater restrictions on abortion and gay rights at an event here on Saturday.

At a forum on moral values, which was held at First Federated, an evangelical church in Des Moines, the six candidates in attendance largely stuck to Republican orthodoxy and avoided criticizing one another. Instead, they called for dramatic changes in current law to achieve conservative aims.

To limit abortion, former House speaker Newt Gingrich, one of the leading candidates in polls here, proposed a federal law defining “personhood” as starting at conception, similar to a provision backed by abortion opponents that was rejected earlier this month by voters in Mississippi. Texas Gov. Rick Perry said he supported provisions that would limit the ability of gay couples to adopt children, while businessman Herman Cain called for changing provisions in the tax code that restrict churches’ involvement in politics if they want to keep their tax-exempt status.

Several committed to supporting state same-sex marriage bans and eventually a constitutional amendment to prohibit it, although libertarian candidate Rep. Ron Paul (Tex.) said the issue should be dealt with by churches and families instead of the government.

“As long as abortion is legal in this country . . . we will never have rest because that law does not comport with God’s law,” said former Pennsylvania senator Rick Santorum.

Gingrich decried a shift toward secularism in America that he called a “disaster.”

“The degree to which the left is prepared to impose intolerance and to drive out of existence traditional religion is a mortal threat to our civilization and deserves to be taken head-on and described as what it is, which is abuse of government to oppress the American people against their own values,” Gingrich said.

The forum, organized by a social conservative group here called The Family Leader, came as polls show a very tight race in Iowa, with four candidates near the top. Gingrich is surging, Paul has shown new signs of strength and Cain and former Massachusetts governor Mitt Romney also remain competitive.

Romney opted against attending the forum, instead campaigning in New Hampshire. Organizers bristled at Romney’s absence, and Bob Vander Platts, head of the Family Leader, predicted before the forum “the next president of the United States will be presenting to you tonight.”

Romney’s no-show was not surprising. He has largely avoided trying to convert conservative, religious voters here who did not back him in 2008 and remain unenthusiastic about him because of his previous support of abortion rights and concerns about his Mormonism.

The event served as a critical test for candidates trying to woo not only the more than 2,000 people who attended in person, but voters who identified themselves as born-again in the 2008 GOP caucuses — more than half the participants. Moderated by longtime political strategist Frank Luntz, it was one of the first events during this primary race to focus on cultural issues instead of economic ones.

Luntz tried to press the candidates on more personal issues, asking them to talk about personal failings or struggles. Gingrich did not directly address his two divorces, but referred to a time in the 1990s when he consulted two Alcoholics Anonymous books, not because he was an alcoholic but because he was “hollow” and “empty.”

“That was really the beginning of turning my life around,” he said.

The candidates attacked liberals and President Obama repeatedly.

Gingrich said his message to the Occupy Wall Street protest movement is: “Go get a job right after you take a bath.”