Boston ? The Massachusetts high court decision endorsing gay marriage raises a host of complex legal questions, and one of the biggest is this: If one state allows same-sex marriages, must other states recognize them?

Experts say it could take years for lawsuits challenging gay marriage to wend their way through state and federal courts, inside and outside of Massachusetts, before ultimately ending up at the U.S. Supreme Court.

Much of the litigation probably will center on the “full faith and credit” clause of the U.S. Constitution, which says states must accept other states’ judicial proceedings.

“People in very short order will move back to Alabama and Tennessee and demand that marriages will be recognized,” said Gary Bauer, president of American Values, a conservative group. “At that point, you have got a constitutional crisis.”

In its 4-3 decision Tuesday, Massachusetts’ Supreme Judicial Court gave the Legislature six months to rewrite the state’s marriage laws for the benefit of gay couples. The effects could soon reverberate across the country.

Experts, however, generally believe the “full faith and credit” argument favors opponents of gay marriage. What little interpretation the U.S. Supreme Court has given indicates the clause applies to legal judgments in “adversarial proceedings” such as lawsuits, and not such things as a marriage license.

Strangely, since divorce is an adversarial proceeding, the Massachusetts divorce of a gay couple could be recognized in other states more easily than their marriage.

The Massachusetts decision also could open the door for challenges to “defense of marriage acts” passed by Congress and 37 states, on the grounds that laws against the recognition of gay marriages violate the rights of gays to equal protection under the Constitution. That was the basis for the U.S. Supreme Court’s recent decision striking down an anti-sodomy law in Texas.

“The meta thing hanging over all of this is the general constitutional question of whether or not states can discriminate against same-sex couples,” said William Eskridge, a law professor at Yale University. “In the near term it’s a state constitutional question. In the longer term, it will loom as a U.S. constitutional question.”

In the hours after the Massachusetts decision was released, Gov. Mitt Romney and several other opponents of gay marriage focused on a state constitutional amendment as the best tool to reclaim marriage as a heterosexual-only institution.

That option, however, could raise even more legal questions, because the earliest voters can amend the state’s constitution is 2006, two years or more after the time the high court has ordered a gay marriage law to be on the books.