Since Newsom argued that the denial of licenses violated the state Constitution, the issue could reach the California Supreme Court. But Uelman said he believed the state's high court would not back Newsom's argument and order gay marriages, as the Massachusetts high court did.
The Rev. Lou Sheldon of the Traditional Values Coalition said his organization was willing to join the lawsuit. He warned that Newsom was dooming other Democrats by raising the issue in an election year, when public opinion shows a backlash against same-sex marriage.
"The mayor has done a very, very stupid thing," Sheldon said, adding that it could be used as a "major wedge issue against incumbent Democrats" in two dozen state Assembly districts.
By late Thursday, more than 80 same-sex couples had recorded their unions. The assessor's office stayed open late to accommodate the long lines as word spread throughout the Bay Area and around the state.
Alexandra D'Amario, 38, and her partner -- 34-year-old Margot McShane -- were among those wed by Teng in front of a crowd of media.
"You are making history and a significant statement in the country and state of California -- that in San Francisco we treat every couple the same way," Teng told them before administering the vows. The couple and Teng then toasted the union with apple juice in plastic cups.
D'Amario, a high school therapist, is pregnant with twins and hopes her partner will be recognized as the children's second parent without having to go through the cumbersome second-parent adoption process that gay and lesbian couples must now complete.
Dale Puri was studying at home Thursday as his partner of two years, Greg George, 54, made some phone calls. A friend called Puri to tell him the news and "I got down on one knee and said, 'Will you run down to City Hall and get married?'" Puri said, as he waited in line for a license.
There were some glitches. Nancy Parsons waited in the clerk's lobby with a dozen red roses for her son and his partner. They had arrived early and obtained a license, but then noticed it read "bride and groom." Employees at the clerk's office scrambled to reissue those documents.
The same-sex application form, where "bride" and "groom" were replaced by "1st applicant" and "2nd applicant," also contains a disclaimer: "Marriage of lesbian and gay couples may not be recognized as valid by any jurisdiction other than San Francisco, and may not be recognized as valid by any employer," it says. "If you are a same-gender couple, you are encouraged to seek legal advice regarding the effect of entering into marriage."
San Francisco already offers generous domestic partner benefits to same-sex couples. But with marriage licenses in hand, the couples can now attempt to seek the array of rights accorded heterosexual married couples -- such as hospital visitation, pensions, healthcare, insurance discounts and other benefits -- throughout California and possibly elsewhere.
Newsom's move could be tested legally if those rights are denied, said Kate Kendell, executive director of the National Center for Lesbian Rights, which is advising the city on its legal position. But Kendell said the legal showdown was more likely to result from a challenge to San Francisco's authority, such as the one the Campaign for California Families planned to file.
That suit, however, will probably have to pass a legal test first -- whether the group has the right to sue city officials.
Stanford University law professor Michael S. Wald said that, to have the right to go to court, a challenger has to be directly affected by the gay marriage. Ackerman, however, said a California court had already ruled that the group had standing to challenge a recent domestic partners law. That challenge is pending.
Hallye Jordan, a spokeswoman for California Atty. Gen. Bill Lockyer, said the office, since the Massachusetts court ruling, had begun studying whether Family Code statutes on marriage violate the California Constitution. But state lawyers have not yet reached a conclusion. As for San Francisco's move, Jordan said, Lockyer would not get involved at this time.
Newsom made his support for same-sex marriage clear during a heated mayoral race last fall. But it was President Bush's State of the Union speech that prompted him to act.
The president's comments opposing same-sex marriage incensed Newsom, said spokesman Peter Ragone, and he formed an advisory team to study what he believed was discrimination forbidden by the state Constitution.
On Thursday, Newsom met privately with Martin and Lyon after the couple wed and handed them a signed copy of the state Constitution, with the equal protection clause highlighted.
"Today a barrier to true justice has been removed," Newsom said in a statement.
It was Kendell, of the National Center for Lesbian Rights, who called the elderly couple earlier this week to offer them the opportunity to be the first same-sex couple in the country to wed legally. The two women helped launch the first national lesbian rights organization and have fought tirelessly for gay equality for decades. They will mark the 51st anniversary of their partnership on Saturday, Valentine's Day.
"We stand on all of their shoulders," Kendell said. "It was a moving experience after a truly lifelong commitment, to have a government entity say, 'Your relationship is valid and important in the eyes of the law.' "
Times staff writers Maura Dolan and Nancy Vogel contributed to this report.