The California Supreme Court today appeared inclined to uphold Proposition 8, but showed obvious reluctance to void thousands of same-sex marriages already in place when voters restored a ban on gay marriage last fall.

During three hours of arguments in San Francisco, the justices peppered lawyers opposing Proposition 8 with questions that suggested they do not believe they have the authority to trump the will of the voters.

At the same time, even justices who voted against striking down California’s previous ban on gay marriage indicated that Proposition 8 should not wipe out an estimated 18,000 same-sex marriages that took place last year. Those couples mobilized around the state to obtain marriage licenses after the Supreme Court ruled last May that California’s prior ban on gay marriage was unconstitutional.

“Is that really fair to people who depended on what this court said was the law?” Justice Ming Chin asked Ken Starr, the former Clinton impeachment prosecutor who argued that same-sex marriages shouldn’t be recognized under Proposition 8.

The justices are considering a high stakes legal challenge to the validity of the measure, which was approved by voters last fall and restored California’s ban on gay marriage. The ballot measure, enacted by a 52 to 48 percent vote, erased last May’s historic state Supreme Court ruling finding California’s prior ban on same-sex marriage unconstitutional because it deprived gay couples of the equal right to wed.

Proposition 8 amended the California Constitution to confine marriage to heterosexual couples, and its backers insist that the Supreme Court cannot overturn the will of the voters if they choose to change the state constitution.

During today’s arguments, the majority of the court remarked that the current case is very different than last year’s, primarily because the voters amended the constitution the court is bound to follow. “I stand by what I said in the marriage cases,” Justice Joyce Kennard, a key vote in legalizing gay marriage last year, said at one point. “But this case is different. We’re dealing with the power of the people.”

Justice Carol Corrigan, who dissented in last year’s decision, remained reluctant to interfere with voters and legislators.

“Is the essence of your argument that the people have the right to amend their constitution as long as it isn’t done in a way the Supreme Court doesn’t like?” Corrigan asked one civil rights lawyer.

Civil rights groups, same-sex couples and a number of local governments, including Santa Clara County and San Francisco, sued to block enforcement of Proposition 8, arguing that it was an improper method of amending the constitution and targets a minority group by depriving gay couples of the right to marry. Attorney General Jerry Brown also has refused to defend the law, saying it is unconstitutional and conflicts with last year’s state Supreme Court ruling.

Christoper Krueger, the senior deputy assistant attorney general who argued for Brown, had the roughest ride during arguments, as all of the justices appeared poised to reject his argument that last year’s ruling created an “inalienable right” for same-sex couples to wed. “What I’m picking up from the argument is that the court should willy, nilly disregard the will of the people,” Kennard told him. “As judges, our powers are limited.”

If the court upholds Proposition 8, the justices must still determine whether existing gay marriages are valid across the state. On that point, even Starr, now dean of the Pepperdine University law school, found himself on the defensive, particularly from Chin and Corrigan, two justices who voted against legalizing gay marriage in the prior case. When Starr tried to maintain the measure had to be read as voiding the marriages, Corrigan shot back, “But this court had said “this is the law in California.”

The justices agreed to review the case in November, producing an avalanche of legal arguments from all sides of the gay marriage debate. The Supreme Court now has 90 days to rule in the case, ensuring the fate of Proposition 8 will be determined before summer begins.

The Supreme Court was divided 4-3 in last year’s ruling, and gay marriage opponents have vowed a political campaign against justices who vote to overturn the ban on same-sex marriage, adding to the intrigue surrounding the high court’s handling of the controversial issue.

Chief Justice Ronald George, who wrote last year’s majority opinion, told a gathering of reporters in December that he ignores such political considerations when he’s deciding a hot-button case. George was joined in the prior ruling by Justices Joyce Kennard, Carlos Moreno and Kathryn Mickle Werdegar. Justices Marvin Baxter, Ming Chin and Carol Corrigan dissented in that case, saying it is up to voters and legislators, not the courts, to change laws governing same-sex marriage.

Contact Howard Mintz at hmintz@mercurynews.com or (408)-286-0236