ST. PAUL — Republican Tim Pawlenty is declining to sign a pledge written by a conservative Iowa group that asks presidential candidates to denounce same-sex marriage rights, pornography and forms of Islamic law.

Pawlenty said Wednesday he agrees with the principles behind the Family Leader’s Marriage Vow, but not the way the 14-point pledge is cast. Earlier in the day, the former Minnesota governor released a new radio ad and a web video in which he and his wife Mary discuss their personal faith, anti-abortion views and opposition to gay marriage.

“Rather than sign onto the words chosen by others, I prefer to choose my own words, especially seeking to show compassion to those who are in broken families through no fault of their own,” Pawlenty said in written statement in which he insists he would “vigorously oppose” any efforts to allow same-sex marriage.

The move is risky for Pawlenty, who is banking heavily on Iowa and its social conservatives to help carry his presidential campaign forward. But signing the pledge could alienate voters who don’t agree with its far-reaching nature.

Pawlenty is the second major candidate in as many days to decline the pledge, following former Massachusetts Gov. Mitt Romney’s decision. Former New Mexico Gov. Gary Johnson and former Utah Gov. Jon Huntsman have also ruled it out. Two Republicans, Minnesota Rep. Michele Bachmann and former Pennsylvania Sen. Rick Santorum, have signed the document.

The Family Leader was formed last year and hopes to have a voice in shaping Iowa’s 2012 leadoff caucuses. Its top officials were part of a successful campaign last fall to remove three Iowa Supreme Court justices who ruled to legalize gay marriage in the state.

Family Leader vice president Chuck Hurley said the group was disappointed Pawlenty bypassed the pledge but took heart by his commitment to its core values.

“If he chooses to use his own words and is convincing with his own words, who knows he may have better words than we do,” Hurley said. “His statement is more than just a tip of the hat. It is an acknowledgement and a pledge that he is going to take the marriage and family issues seriously.”

Pawlenty advocated for a constitutional amendment in Minnesota to define marriage as between a man and a woman. But as governor, he didn’t have a role in advancing any such legislation to the ballot. Minnesota voters will decide the question in November 2012.