San Francisco's defiant choice to perform same-sex marriages by the hundreds is reverberating nationwide as gay-rights groups celebrate, their adversaries hope for a backlash and politicians wrestle with how to respond.

Mayors in Chicago, Salt Lake City and upstate New York spoke favorably of the weddings, but many politicians — including some liberal Democrats — are unsettled by the spectacle of more than 2,700 gay and lesbian couples wed over the past week at San Francisco's city hall.

Sen. Barbara Boxer, D-Calif., an outspoken supporter of gay rights, issued a terse statement that offered no praise for San Francisco Mayor Gavin Newsom. Rep. Barney Frank, D-Mass., one of three openly gay members of Congress, suggested Newsom's action could undermine long-term efforts to legalize gay marriage in Massachusetts and fuel support for a federal constitutional amendment banning such unions.

On the Republican side, President Bush said the San Francisco weddings troubled him, and could influence his decision on whether to support the proposed constitutional amendment.

Yet some conservative groups felt both Bush and California's Republican governor, Arnold Schwarzenegger, were being too timid.

"A real terminator would end the anarchy by enforcing the law he swore an oath to uphold," said Jan LaRue, chief counsel for Concerned Women for America, in reference to Schwarzenegger — who asked Newsom to stop the marriages. LaRue's organization said the Justice Department and California officials should consider launching criminal proceedings against the San Francisco mayor and his staff for performing illegal marriages.

The Lambda Legal Defense and Education Fund, a gay-rights organization, said it had analyzed relevant California laws and determined that threats of criminal action "are groundless and should be ignored."

"These kinds of wild assertions. ... seem designed only to frighten couples and city workers," said Jon Davidson, a Los Angeles-based senior counsel for Lambda Legal.

Meanwhile, the city of San Francisco said Thursday it is suing the state of California, challenging its ban on same-sex marriages on constitutional grounds.

Even before the San Francisco weddings, gay marriage had emerged as a volatile election-year topic, largely because of the Massachusetts Supreme Judicial Court's ruling last year that the state must start recognizing gay marriages as of May 17.

"Where's the rule of law?" asked Tony Perkins, president of the conservative Family Research Council. "You have judges acting like legislators in Massachusetts, and you have a mayor acting like a judge in San Francisco. They need to go back and read their job descriptions."

He predicted a surge of support for the proposed amendment banning gay marriage as non-California couples who wed in San Francisco return home and seek recognition of their unions.

There were no immediate reports of other elected officials emulating Newsom by authorizing same-sex marriages, but a handful of mayors made supportive comments.

Chicago Mayor Richard Daley said he would have "no problem" with Cook County issuing same-sex marriage licenses. Regarding gay couples, Daley said, "They love each other just as much as anyone else."

In Plattsburgh, N.Y., the openly gay mayor said he supports same-sex marriage even though many of his fellow Republicans differ.

"I am on the opposite side of this issue — I understand that — but, as a gay man, I have to fight for equality," Daniel Stewart told the Press-Republican of Plattsburgh.

Salt Lake City Mayor Rocky Anderson, an honorary board member of the pro-gay-marriage group Freedom to Marry, said he welcomed the developments in San Francisco and Massachusetts.

"The more people become familiar with the impacts of marital discrimination on so many people, the greater progress we're going to see," Anderson said.

In New York City, a spokesman for Mayor Michael Bloomberg said that, though a supporter of gay rights, the mayor had no intention of following Newsom's path.

"The mayor does not believe in subverting the law to make a political point," spokesman Ed Skyler said.

Matt Coles, director of the American Civil Liberties Union's Lesbian and Gay Rights Project, said the Massachusetts case, rather than the San Francisco action, was more likely to survive legal challenges and lead to permanently recognized same-sex marriages.

"However, this fight ultimately is about what America thinks is fair, and in that sense Mayor Newsom has done a great service," Coles said. "Americans watched on television as hundreds and hundreds of people stood in the pouring rain all night to get married, and a fair number of them probably thought, 'Gee, we didn't have to go through that."'