The U.S. Supreme Court hears arguments Tuesday in a case that could legalize same-sex marriage in the 13 states that now prohibit it. But the stakes are potentially just as high in many of the 37 states, including California, that now allow gays and lesbians to wed.

That’s because marriage rights in 26 of those states were secured by lower-court rulings that the Supreme Court has previously declined to review. Those rulings could be erased, and same-sex marriage bans reinstated, if the high court now decides that states have the constitutional authority to enact such laws.

“If there is no United States constitutional right to marriage equality, states will be able to prohibit same-sex marriage” under their own laws, said Erwin Chemerinsky, the law school dean at UC Irvine and a liberal legal commentator who has argued cases before the high court.

State laws against same-sex marriage, like California’s Proposition 8, remain on the books despite federal court rulings barring their enforcement.

Back to Gallery Same-sex marriage hinges on U.S. Supreme Court decision 6 1 of 6 Photo: Mary F. Calvert, Special to the Chronicle 2 of 6 Photo: Mary F. Calvert, Special to the Chronicle 3 of 6 Photo: Mary F. Calvert, Special to the Chronicle 4 of 6 Photo: Mary F. Calvert, Special to the Chronicle 5 of 6 Photo: Mary F. Calvert, Special to the Chronicle 6 of 6 Photo: Mary F. Calvert, Special to the Chronicle











If the Supreme Court upholds similar laws from four states in the current case, “it would wipe out” the lower-court rulings and state bans “would become enforceable again,” said Ed Whelan, a conservative commentator and president of the nonprofit Ethics and Public Policy Center.

Whelan said governors in those states could even refuse to recognize same-sex marriages that had already taken place. Other commentators disagreed, saying courts would probably let couples rely on the previous rulings that allowed them to marry.

California’s situation

The situation could be different in California, because Gov. Jerry Brown and Attorney General Kamala Harris declined to defend Prop. 8, the state constitutional ban on same-sex marriage that voters approved in 2008. Chief U.S. District Judge Vaughn Walker ruled Prop. 8 unconstitutional in 2010, and his ruling became final three years later when the Supreme Court said the ballot measure’s sponsors had no standing to appeal.

But if the Supreme Court now decided that laws like Prop. 8 were constitutional, Brown and Harris would have a legal obligation to enforce the ban, said A.E. Dick Howard, a law professor at the University of Virginia widely respected as an authority on constitutional law. That would also be true in other states, like Oregon, Nevada and Virginia, whose top executives declined to defend their marriage laws, he said.

If the Supreme Court upholds a state’s authority to ban same-sex marriage, Howard said, “it’s hard for me to imagine a governor or attorney general” refusing to enforce a similar law in another state, despite their personal views.

That would mean gays and lesbians in California would again be prohibited from marrying until at least November 2016, when the issue would likely return to the state ballot. Legislative wars over marriage would also be renewed in other states.

Experts’ predictions

In interviews with about a dozen legal commentators, most said they wouldn’t rule out a Supreme Court decision upholding the state laws, but they don’t think it’s the most likely result. As the court prepares to hear cases from Ohio, Michigan, Kentucky and Tennessee, whose bans on same-sex marriage were upheld by a federal appellate court in November, there have been signals that a majority of justices are willing to find all such laws unconstitutional.

The first sign was in the 2013 ruling striking down the central provision of the Defense of Marriage Act, which denied federal benefits to married same-sex couples. Swing-vote Justice Anthony Kennedy said the federal law relegated gay and lesbian couples to a “second-tier marriage” and “humiliates tens of thousands of children.”

Although Kennedy steered clear of endorsing a right to marry, dozens of lower-court judges have interpreted his words as an invitation to a broader ruling.

390,000 marriages

That’s the main reason the number of states allowing same-sex marriage, which was nine at the time, has more than quadrupled. According to the Williams Institute at UCLA, the number of same-sex married couples in the nation has tripled, to 390,000.

In October. the court surprised most legal analysts, and heartened gay-rights advocates, by declining to review rulings by four federal appeals courts declaring same-sex marriage bans unconstitutional. The justices took up the issue this year only after an appeals court in Cincinnati upheld marriage restrictions in November, further increasing expectations of a ruling in June that would prohibit such laws in any state.

“The likelihood of the court upholding the restrictive laws is pretty slight at this point,” particularly in view of the “chaos” that would ensue in other states, said Rick Banks, a Stanford law professor.

On the other hand, this is, by most assessments, the most conservative Supreme Court since the 1930s, and one that has pointedly refrained from addressing same-sex couples’ right to marry. The justices raised a second question in this case — whether a state that bans same-sex marriage can refuse to recognize marriages performed elsewhere — and could easily choose to address only that question while “punting” the broader marriage issue, said Paul Collins, director of legal studies at the University of Massachusetts-Amherst.

Some commentators noted that Kennedy, author of the court’s major rulings on gay rights, is also an advocate of “federalism,” which elevates the authority of the states rather than the federal government to decide social issues. That was a theme of his 2013 opinion on the Defense of Marriage Act, and — as the University of Richmond’s Carl Tobias pointed out — the crux of his 2014 opinion upholding Michigan’s ban on racial considerations in public college admissions, a law similar to California’s Proposition 209.

The central question in that case, Kennedy wrote, was not how the racial debate should be resolved, but “who may resolve it.” The Constitution, he said, respects a state’s decision to “commit this policy determination to the voters.”

GOP lawmakers’ brief

The four states and their supporters have invoked federalism in their arguments to the court. A brief signed by 57 Republican members of Congress, including Senate Majority Leader Mitch McConnell of Kentucky, contends that a nationwide decree overriding state marriage laws “would circumvent the proper resolution of these profound and divisive issues through state democratic processes.”

The states also argue that their laws are based on tradition and family values, not discrimination. A vehement version of that position comes from Protect Marriage, the group that sponsored California’s Prop. 8.

Its lawyer told the Supreme Court in the current case that overturning same-sex marriage bans on the grounds that they are based on discrimination could be seen as judicial endorsement of “the hate and contempt many advocates of redefining marriage hold for those who disagree with them.”

Couples seeking the right to marry are focusing on the state laws’ harsh impact on their households, another theme of Kennedy’s in the 2013 case.

The main purpose and effect of Kentucky’s law is to “brand same-sex couples and their families as less worthy than other families,” argued the plaintiffs’ lawyers, who said their clients “ask merely to be treated like everyone else.”

Their allies include President Obama’s Justice Department, which argued that laws discriminating on the basis of sexual orientation should be scrutinized closely and skeptically by the courts. That standard, which now applies to sex discrimination, could be used to overturn laws in more than half the states allowing employers to fire gays and lesbians, and allowing retail stores to refuse to serve them.

Some religious conservatives are already making plans to defy a ruling legalizing same-sex marriage. A “marriage pledge” circulated by Liberty Counsel and other groups declares that male-female marriage is divinely ordered, and vows “obedience to our creator when the state directly conflicts with higher law. We respectfully warn the Supreme Court not to cross this line.”

Newsom will attend

Also anticipating such a ruling is Lt. Gov. Gavin Newsom, who is attending Tuesday’s hearing. As San Francisco mayor in 2004, Newsom defied state law by ordering city clerks to issue marriage licenses to same-sex couples. That led to 4,000 marriages that the state Supreme Court nullified, another legal case in which the court briefly legalized same-sex marriages in California, and then to Prop. 8 and the ensuing four-year federal court battle.

A few years ago, Newsom said, he was starting to think that “maybe the critics were right, that this was too much, too soon and too fast. But thousands of people didn’t get the word. They weren’t told change was impossible.”

Robert Egelko is a San Francisco Chronicle staff writer. E-mail: begelko@sfchronicle.com Twitter: @egelko