Gov. Rick Perry on Friday became the latest Republican presidential candidate to sign a pledge to support an amendment to the Constitution that would outlaw gay marriage. His pledge came a month after he voiced support for the right of states to decide for themselves about gay marriage and other social issues.

The National Organization for Marriage pledge states that, if elected, Perry will send to the states for ratification a constitutional amendment defining marriage as the union of one man and one woman. He also pledged to appoint U.S. Supreme Court judges and federal judges who will "reject the idea our Founding Fathers inserted a right to gay marriage into the Constitution."

"The purpose of NOM's Marriage Pledge is to move from vague values statements to concrete actions to protect marriage. Gov. Perry joins Michele Bachmann, Mitt Romney and Rick Santorum as a signer of NOM Marriage Pledge," said Brian Brown, president of the organization, in a statement. "By doing so, Perry makes crystal clear that, contrary to the conventional wisdom, gay marriage is going to be a bigger issue in 2012 than it was in 2008, because the difference between the GOP nominee and President Obama is going to be large and clear."

Perry also signed a pledge this week offered by an anti-abortion group called the Susan B. Anthony List that commits him to selecting only "strict constructionist" judges and anti-abortion appointees to Cabinet and executive branch positions. By signing the pledge he also commits to an effort to de-fund Planned Parenthood and to sign a Pain Capable Unborn Child Protection Act.

Perry's signature on the anti-abortion pledge is consistent with positions he has taken throughout his career, but he has had to scramble since becoming a presidential candidate to clarify his position on gay marriage.

Speaking to a Republican Governors Association forum in Colorado last month, a few days before he declared his candidacy, he said that his strong support of state's rights meant that he could accept New York's approval of gay marriage, even though he still considered himself an "unapologetic social conservative."

"Our friends in New York six weeks ago passed a statute that said marriage can be between two people of the same sex," he told the Colorado gathering. "And you know what? That's New York, and that's their business, and that's fine with me. That is their call. If you believe in the 10th Amendment, stay out of their business."

Adding a few words

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Social conservatives immediately took issue with Perry's position.

"So, Gov. Perry, if a state wanted to allow polygamy, or if they chose to deny heterosexuals the right to marry, would that be OK, too?" former Sen. Rick Santorum tweeted. Santorum also is seeking the GOP nomination for president.

A week later, Perry told Family Research Council President Tony Perkins, "I probably needed to add a few words after that 'it's fine with me,' and that it's fine with me that a state is using their sovereign rights to decide an issue. Obviously, gay marriage is not fine with me. My stance hasn't changed. I believe marriage is a union between one man and one woman."

He told Perkins he had worked to pass a defense of marriage act in Texas and had signed a bill in 2003 specifying that Texas does not recognize same-sex marriage or same-sex civil union.

He also told Perkins he was in favor of a federal marriage amendment as a way to thwart "activist" judges.

His book Fed Up! Our Fight to Save America from Washington, would seem to tolerate differences among the states: "If you don't support the death penalty and citizens packing a pistol, don't come to Texas. If you don't like medical marijuana and gay marriage, don't move to California. ... I would no more consider living in Massachusetts than I suspect a great number of folks from Massachusetts wold like to live in Texas. We just don't agree on a number of things. They passed state-run health care, they have sanctioned gay marriage."

The pledge factor

More interest groups this campaign season are insisting that candidates sign pledges to gain endorsements and donations. Although Democrats occasionally are asked to sign pledges, it primarily is a Republican phenomenon.

GOP candidate Jon Huntsman, a former Utah governor, has pledged not to pledge.

"I don't sign pledges - other than the Pledge of Allegiance and a pledge to my wife," he said while campaigning in Idaho recently.

joe.holley@chron.com