SAN FRANCISCO — Same-sex marriage is history in California.

That was quickly apparent Thursday when two justices who backed marriage for gays and lesbians last year signaled they intend to uphold the measure that took that right away.

Chief Justice Ronald George and Justice Joyce Kennard, who helped form the 4-3 majority that let same-sex couples wed for six months last year, gave all indications that Proposition 8 — as unpalatable as it might be to them — must be accepted as the will of the people.

“Our task is quite limited,” Kennard told anti-Prop 8 lawyers during oral arguments in San Francisco. “The people are those who have created the Constitution and what you are overlooking is the people’s broad power to amend the Constitution.”

George echoed those thoughts, even though he hinted that the Constitution — which he noted has been amended more than 500 times in California history — might be too easy to change.

“Isn’t that the system we have to live with?” he asked, suggesting that any change in the initiative process would have to come from the political realm, not the courts.

Arguments in the three separate cases heard Thursday were presented by five attorneys opposed to Prop 8 and one favoring it. A 5-2 vote upholding the measure, which was passed by voters on Nov. 4, seemed imminent. The only holdouts might be Justices Kathryn Mickle Werdegar and Carlos Moreno, who sounded sympathetic to gay-rights lawyers’ arguments that Prop 8 was a revision, not an amendment, to the state Constitution and thus required a two-thirds majority vote in the state Legislature.

Gay-rights lawyers claim Prop 8 was a revision because it took away a fundamental right from gays and lesbians, a group the Supreme Court’s marriage ruling defined as a suspect class deserving greater protections. But Prop 8 proponents contend that in past cases, “revision” has been understood as a major structural change affecting the workings of the government, not individual rights.

“But this is new to us,” Werdegar told Pepperdine University School of Law Dean Kenneth Starr, who argued to uphold Prop 8. “This is the first time the argument has been made to this court to look at revisions under a different light for a different problem.”

Just because past cases have held that revisions involved structural change to the government, Werdegar added, “doesn’t mean we’ve said it must be a structural change.”

Gays and lesbians can take comfort in the fact that the justices indicated that the 18,000 same-sex marriages that took place before Prop 8 are safe.

Even the three justices who voted against gay marriage last year appeared reluctant to invalidate marriages already performed. After all, they said, the Supreme Court told couples they could wed.

“Aren’t the people who relied on the constitutional pronouncement of this court,” Justice Carol Corrigan asked, “entitled to rely on the law that existed at the time they married?”

The arguments immediately got off on the wrong foot for gay-rights lawyers like Shannon Minter, legal director for San Francisco’s National Center for Lesbian Rights, who ran into quick resistance to his arguments about Prop 8 being an impermissible revision.

The chief justice didn’t seem to buy Minter’s argument that ballot initiatives could stand only if they improved the Constitution rather than take away rights. He posed a hypothethical in which same-sex marriage wasn’t upheld by the court, and then was followed by two initiatives — one that legalized such marriages and a subsequent one that outlawed them.

Wouldn’t it be a “one-way street,” he asked, if one group was allowed to extend rights while another was prohibited from removing them?

George also hammered home the point that, in his view, Prop 8 only denied same-sex couples the label of marriage. It didn’t affect the court’s ruling that gays and lesbians constitute a suspect class, he said, and didn’t eliminate all the rights offered by domestic partnerships.

Kennard lashed out a couple of times over assumptions that she would invalidate Prop 8 just because she voted for same-sex marriage last year.

“This case is different,” she told San Francisco Chief Deputy City Attorney Therese Stewart. “Here we are dealing with the power of the people — an inalienable right for the people to amend the Constitution.”

Kennard told Stewart that the state has a “pretty well-established body of law pertaining to what is or isn’t a revision. Those rulings don’t give strong support to your argument.”

Sacramento-based Supervising Deputy Attorney General Christopher Krueger had the difficult task of arguing against Minter’s and Stewart’s revision theory, while contending that Prop 8 nonetheless violated the Constitution by depriving a suspect class the inalienable liberty right of marriage.

That set off an entire debate about what constitutes inalienable rights.

“How do you define that word?” George asked. “Is it different from an inviolate right? What is that type of right?”

George pulled out the Constitution to point out that it guarantees the right to fish and access to navigable waterways, rights that don’t seem that weighty.

Justice Marvin Baxter asked whether the people have an inalienable right to be free from cruel and unusual punishment. He then cited People v. Anderson , 6 Cal.3d 628, in which the California Supreme Court in 1972 ended the death penalty by calling it cruel and unusual punishment. A few years later, he said, the voters approved an initiative that reinstated it anyway.

“So,” Baxter continued, “if the people passed an initiative to execute in the most cruel manner possible, is that OK?”

Starr took a tough stance when Werdegar insinuated that amending the Constitution to remove individual rights might be as significant as amending it to deprive a government institution, such as the Supreme Court, of some of its powers — as did a 1990 initiative that was declared unconstitutuional.

“Rights are important, but they don’t go to structure,” Starr said. “If you tinker with the structure and undermine the authority of this court, you’ve gone too far. But, your honor, rights are ultimately defined by the people.”

Starr raised a few eyebrows when he suggested that voters could likely ban anti-discrimination laws, prevent gays from adopting children, and just about any other thing they want — as long as it doesn’t affect government structure.

“Under our theory,” he said, “the people are sovereigns and can do unwise things.”

Starr ran into a real buzz saw, though, when he argued that marriages performed between the court’s ruling last year and the passage of Prop 8 shouldn’t stand.

“We do not believe Prop 8 invalidates [those marriages],” he argued. “What it does do is deny recognition.”

That didn’t sit well with any of the justices. “Is that fair to the people who depended on the court’s ruling?” asked Justice Ming Chin.

While the three-hour arguments were under way, hundreds of anti- and pro-Prop 8 forces chanted in the streets outside the court. Many watched on a Jumbotron in front of City Hall, while dozens more watched in various locales within the court building itself.

Minter wouldn’t concede that the arguments didn’t go well for his side, but admitted that Kennard “was not inclined to accept our argument.”

Starr didn’t speak afterward, but Robert Tyler, the Murietta-based general counsel for Advocates for Faith & Freedom, which backed Prop 8, said he was encouraged by the arguments. He especially thought Kennard “expressed from the bench the importance of the people’s sovereignty.”

A ruling is due within 90 days. The cases are Strauss v. Horton , S168047; Tyler v. State of California , S168066; and City and County of San Francisco v. Horton , S168078.