Legal experts say California's same-sex weddings could be fertile ground for a bumper crop of lawsuits and government claims from coast to coast.

If California voters in November approve an amendment banning same-sex marriages, the courts will have to decide what to do about those already solemnized. And the amendment aside, couples who marry here and then go elsewhere could be on uncertain legal ground.

"The one thing we're sure of is that there will be a lot of litigation," said Brad Sears, executive director of the Charles R. Williams Institute on Sexual Orientation Law and Public Policy, a think tank at the UCLA School of Law.

Factors "weigh fairly strongly in favor of recognizing marriages that occur between June and November" even if the amendment passes and halts same-sex marriages thereafter, he said.

California courts usually don't apply new laws or constitutional amendments retroactively unless they're explicitly worded to be retroactive, Sears said.

The courts would probably consider the third parties affected by suddenly voiding thousands of marriages: a child who gains a parent by such a marriage, for example, or perhaps a bank that granted a mortgage to a married couple.

Stanford Law School professor Jane Schacter, an expert in constitutional law as well as in sexual orientation and the law, said she thought "the marriages will not be retroactively invalidated."

Marriages solemnized when San Advertisement Francisco Mayor Gavin Newsom told city officials to issue licenses to same-sex couples in 2004 were voided because they had directly violated state law as it existed at that time. Schacter said it's hard to believe California courts would take the "extraordinary step" of voiding marriages that were valid when performed.

The legal rights and benefits afforded to California's same-sex married couples won't differ enormously from those already afforded to domestic partnerships, except for the abolition of what critics had called a "separate but equal" system created by the different terms. There are a few advantages; for example, same-sex couples can now enter into a confidential marriage — one that's not a matter of public record — while all domestic partnerships had to be publicly listed.

Federal law, however, still doesn't recognize spousal rights or benefits for same-sex couples whether the state calls it marriage, domestic partnership or anything else.

As for couples from elsewhere, Schacter said, "in most states couples who come to California to marry are going to have an uphill battle getting those marriages recognized."

There are exceptions. Massachusetts and California will recognize each other's same-sex marriages, Sears said, and New Jersey and New Hampshire likely will treat California's as civil unions under their own laws. New York state agencies have been instructed that same-sex couples married elsewhere "should be afforded the same recognition as any other legally performed union."

Sears said New Mexico has a similar legal backdrop to New York's: no law or constitutional amendment barring recognition; a state law defining marriage as between two adults, not explicitly a man and a woman; and strong language on recognizing marriages performed in other states.

Most other states have laws or constitutional amendments barring recognition of same-sex marriages, Sears said.

But legal gray areas could exist there, too, he said. For example, such a state might refuse to provide ongoing benefits predicated on marriage, yet might be inclined to allow one-time proceedings such as divorces.

There's also the question of "traveling cases," such as if a same-sex couple married in California were in a car accident and try to exercise marital legal rights while passing through another state with different laws. Sears said, "It seems unlikely your relationship is going to flick on and off as you travel across the country."

And, Schacter said, "lurking around the background are some possible federal constitutional challenges," perhaps tackling the federal Defense of Marriage Act — which says states need not honor other states' same-sex marriages — either as a denial of equal protection or as a violation of the "full faith and credit" clause requiring states to honor one another's laws.

But Schacter noted same-sex-marriage advocates have shied away from such challenges thus far. In fact, nine major gay-rights groups issued a memo Tuesday urging people not to pursue such suits, warning they could bring about "bad" rulings that could stand for years to come. They said it's better to keep the matter before state courts and legislatures for now.