The U.S. Supreme Court’s forthcoming ruling on Proposition 8, California’s ban on same-sex marriage, could follow any of at least half a dozen complex scenarios.

The high court decision is expected sometime before the close of the court’s current term at the end of this month.

One scenario is that the panel would uphold the 2008 voter initiative restricting marriage in California to the union of a man and a woman.

In that outcome, a court majority could agree with Proposition 8 sponsors’ claim that state voters had the right to conclude the ban would “increase the likelihood that children will be born and raised in stable and enduring family units by their own mothers and fathers.”

On the other side, there are at least five ways that the high court could invalidate Proposition 8, for reasons related either to the merits of the arguments or to court procedures.

In any of those scenarios, an urgent question for county clerks’ offices and couples seeking to marry would be how soon same-sex weddings might resume in California.

San Francisco City Attorney Dennis Herrera answered that question today in a formal memorandum to the county clerk’s and assessor-recorder’s offices, which license and register marriages.

The most likely time that gay and lesbian weddings could resume would be sometime between the middle and end of July, Herrera said.

“You should be prepared to issue licenses to same-sex couples in mid-to-late July” if Proposition 8 is taken off the books, he advised the city officials.

Herrera wrote that the time estimate includes a 25-day period in which a losing party can ask the U.S. Supreme Court to reconsider a case, plus an additional several days for the 9th U.S. Circuit Court of Appeals in San Francisco to resume jurisdiction over the case.

In previous rulings, both the appeals court and a federal trial judge in San Francisco struck down Proposition 8, although for different reasons.

The measure’s sponsors appealed to the Supreme Court after losing in the lower courts, and the panel’s nine justices heard arguments on March 26. The case stems from the federal civil rights lawsuit filed in 2009 by two same-sex couples who want to marry.

Among the scenarios in which the high court could invalidate Proposition 8, there are three ways in which the court could rule on arguments of legal substance, known as ruling on the merits.

Most broadly, a court majority could agree with the reasoning of now-retired U.S. District Judge Vaughn Walker, who said in 2010 that the U.S. Constitution provides a right to gay marriage.

Such a ruling would apply nationwide. But a broad decision is now considered unlikely, since the justices during the March arguments appeared to be seeking a cautious approach.

Most narrowly, a majority could agree with last year’s 9th Circuit ruling, which would apply only to California. The circuit court said that since gay marriage was legal in California for several months in 2008, it was unfair for voters to withdraw that right for no apparent reason other than hostility toward gay people.

A middle ground could be to adopt the rationale argued by the U.S. Justice Department, which would apply to California and seven other states.

That rationale is that in states that allow domestic partnerships and civil unions similar to marriage, it is unfair to deny same-sex couple the name and status of marriage.

Finally, the Supreme Court could nullify Proposition 8 on either of two procedural grounds.

One is to avoid a ruling and instead dismiss the case as “improvidently granted,” meaning that the court should not have taken up the appeal.

That option would leave the 2012 9th Circuit ruling in place, allowing gay marriages in California under a rationale that would apply only to the Golden State. (California would, however, be added to 12 other states that now recognize same-sex marriage because of other court decisions, voter initiatives or state laws.)

The second and last procedural option is that a court majority could conclude that Proposition 8’s sponsors lacked the standing, or legal authority, to appeal to the 9th Circuit.

The sponsors sought to step in to appeal after the lawsuit’s original defendants, including Gov. Jerry Brown and state Attorney General Kamala Harris, declined to appeal Walker’s ruling.

A high court decision that the sponsors lacked standing to appeal would leave in place Walker’s trial court decision that Proposition 8 violated the constitutional rights of due process and equal treatment.

But the two sides disagree on what would happen next. Lawyers for Proposition 8’s sponsors contend Walker’s decision would allow marriage only for the two plaintiff couples, Kristin Perry and Sandra Stier of Berkeley and Paul Katami and Jeffrey Zarrillo of Burbank.

The couples and the city of San Francisco contend that an injunction issued by Walker against state officials would apply statewide and that all same-sex couples in California would have a right to marry.

Herrera advised city officials in his memo that a no-standing decision by the Supreme Court might result in more legal disputes about the effect of that decision, but said, “We are confident that we would prevail in any litigation challenging the scope of the injunction.”

Herrera said that if left in place, Walker’s conclusion that Proposition 8 was unconstitutional “by definition means that there is no set of circumstances in which the government could constitutionally apply” the measure.

Julia Cheever, Bay City News