Facing declining poll numbers, the president is likely with his new stance to shore up his conservative base - for which banning gay marriage is a priority. He is banking on polls that show, in general, that Americans oppose gay marriage by up to a 2-to-1 margin.

The polls, though, show much ambivalence on the subject, with many who oppose gay marriage also opposed to a constitutional amendment.

"By and large, in most polls, majorities say, 'Leave it to the states,'" said Carroll Doherty, editor of the Pew Research Center.

In fact, Vice President Dick Cheney, whose daughter Mary is openly gay, said during the 2000 presidential campaign that the states, not the federal government, should decide whether to recognize same-sex relationships. Last month, he said he had not changed his position but would support whatever decision Bush made on the topic.

Doherty said Bush is trying to place himself in the middle - by stressing that he was forced to intervene because of activist judges and local officials and by not ruling out civil unions. But Doherty said he sees "real potential for a backlash" among moderate Republicans and independent voters who might see Bush as intolerant.

In a new poll by the University of Pennsylvania's National Annenberg Election Survey, 64 percent of the respondents said they would oppose laws allowing same-sex marriage in their states; 30 percent said they would back such laws. But when asked about a constitutional amendment to bar states from enacting same-sex marriage laws, 41 percent supported it and 48 percent opposed it.

A spokesman for the Log Cabin Republicans, a gay organization that backed Bush in 2000, said the president's move would likely cost him the group's support this time.

"If you're going to promote family values, then you have to value all families," said Mark Mead, the group's spokesman.

Though Kerry opposes gay marriage - and has said he disagrees with his state's high court decision - he was one of 14 senators who voted against the 1996 Defense of Marriage Act. That measure defined marriage as a union between a man and a woman, and it let states deny recognition of same-sex marriages sanctioned by other states. Republicans are likely to use Kerry's vote to portray him as left of the mainstream.

Bush said a constitutional amendment is needed because the Defense of Marriage Act, which passed Congress overwhelmingly and was signed by President Bill Clinton, has been eroded by courts and local officials.

The president did not endorse any particular wording yesterday. But he is said to embrace a proposal by Rep. Marilyn Musgrave, a Colorado Republican, stating that "Marriage in the United States shall consist only of the union of a man and a woman."

The gay marriage issue cuts across legal and religious, as well as social and political lines, and yesterday, Maryland's religious community reflected the nation's split. The Rev. William Kopp, pastor of Riverside Baptist Church in Baltimore, said he was relieved by the news and pleased to see Bush take a strong moral stand on the issue after weeks of hesitation.

"I'm a local pastor, and I believe homosexuality is against God's plan for his people, [but] I'm never surprised by what the world is going to do out there," said Kopp, an evangelical. "A constitutional amendment would certainly resolve many of the issues we face nationwide."

On the other side was Martha Horn, a lay preacher at St. George's Episcopal Church in Prince George's County, who said she found Bush's decision "appalling."

"To amend the Constitution - I mean, what's that going to mean for us?" said Horn, who plans to travel to Massachusetts to marry her longtime partner. "Life, liberty and the pursuit of happiness - unless you are a gay or lesbian person?"

Sun staff writer Frank Langfitt contributed to this article.