From the first moment of the first television commercial of his campaign for governor of Indiana, Eric Miller (search) could not have been plainer about his opposition to gay marriage, the simmering social issue of the election year.

The conservative Republican "is fighting to protect marriage in Indiana," the ad said. "Marriage should be between a man and a woman."

Nor is Miller alone in spotlighting gay marriage in his campaign. A small number of conservative Republicans have done likewise in the two months since gays and lesbians lined up to obtain marriage licenses in San Francisco and other cities, and President Bush called for a constitutional ban on same-sex nuptials.

"I want to go to Congress to help President Bush restore our economy, strengthen health care, preserve the sanctity of marriage and protect our way of life," George Moretz (search) declared in a commercial touting his bid for the Republican nomination in a congressional race from North Carolina.

"You can count on me to help President Bush pass a constitutional amendment banning same-sex marriages," said an ad for Chris Mathys (search), who last month lost his bid for the GOP nomination to a legislative seat in California.

"To me, a marriage will always be a union between a man and woman," first-term Rep. John Carter of Texas said in an ad that was part of a successful campaign for renomination.

To date, the references have been made gingerly, so much so that commercials typically mention preserving the "sanctity of marriage" or "protecting marriage" rather than opposition to gay marriage. Republican strategists say that while public polling shows overwhelming opposition to same-sex marriages, candidates risk offending swing voters if they appear intolerant or strident in addressing the issue.

Like Mathys, several candidates who make mention of the issue do so in the context of supporting Bush. "I will support the president's constitutional amendment to protect traditional marriage," said an ad for Ben Streusand, who lost a congressional primary in Texas earlier this month.

Several of the ads have aired in Republican congressional primaries across Southern states, home to some of the nation's most conservative voters. At the same time, said Rep. Jim DeMint (search), R-S.C., "It is an issue that has gotten the attention of a far bigger group than just the religious right."

DeMint, competing in a crowded field for the GOP senatorial nomination, says in an ad: "We don't need to redefine marriage to make sure everyone has equal rights. We've got to protect the sanctity of marriage and recognize and protect the sanctity of life."

He said he included the issue in a campaign commercial because he feels strongly about it personally, and to present himself and his views to voters across South Carolina who are unfamiliar with him. "It's letting people know who I am."

Miller, seeking the gubernatorial nomination in Indiana, said it was no accident that his commercial opens with a mention of gay marriage. "In the governor's race it has given me an issue where I can differentiate myself from my Republican opponent and the Democratic governor," he said in an interview.

He said he is the only candidate in the race who supports a constitutional amendment to ban both gay marriages and civil unions.

Miller, the underdog for the Republican gubernatorial nomination in a race with former Bush administration budget director Mitch Daniels, said a proposed constitutional amendment cleared the GOP-controlled Indiana Senate but was bottled up in the Democratic-run state House.

"That makes it a huge issue as we head for election," Miller said, signaling an intention to continue to stress the issue if he wins the nomination.

While Bush called on Congress to approve a constitutional amendment, the issue has not been included in any of his commercials. One senior aide, speaking on condition of anonymity, said it is unlikely to play a role in the president's general election campaign advertising, even though Democratic rival and Massachusetts Sen. John Kerry, opposes the measure.

But that doesn't mean it will necessarily disappear once the Republican primaries are over.

"If it remains a front-burner issue in the national media it will remain a front-burner issue in Texas politics," Rep. Carter said.

Mark Stephens, campaign consultant to Moretz in North Carolina, also said it was possible some Republicans might run against Democrats in part by trying to link them to Kerry's opposition to the amendment.

"If it's a position that the vast majority of the voters in that state or in that congressional district or in that region of the state would agree with then certainly it might be grounds to take up the issue in the fall," he said.