WASHINGTON -- The Supreme Court wades into a wide array of same-sex marriage cases Friday, and its selections could put an exclamation point on a year of unprecedented progress for the gay-rights movement.

The nine justices must decide which case or cases to consider from among seven on their plate, from the right to marry in California to the receipt of federal marriage benefits from coast to coast.

While oral arguments and court rulings would be months away, just the choices made in Friday's closed-door conference could doom California's troubled Proposition 8 ban on same-sex marriage or put the federal Defense of Marriage Act on the defensive.

All lower court decisions thus far have upheld the rights of gay and lesbian plaintiffs. Rulings that the high court refuses to reconsider will stand. Any it schedules for early next year would have recent case law stacked in its favor.

The court is virtually certain to take up at least one of the cases involving the 1996 Defense of Marriage Act, which defined marriage in federal statutes as between a man and a woman. That's because the lower courts from California to New England have struck down a key section of the law, inviting a Supreme Court decision. The impact of that section has been to deny federal assistance, such as tax exclusions and Social Security survivor benefits, to gay and lesbian couples.

Less certain is whether the justices will consider California's Proposition 8, approved by voters in 2008 but since declared unconstitutional by two federal courts. If they don't, gays and lesbians in the nation's largest state will be able to marry again, as 18,000 couples did before the referendum was passed.

The flurry of court action comes just three weeks after voters approved same-sex marriage initiatives in Maine, Maryland and Washington, bringing to nine the number of states where those unions are legal, along with the District of Columbia. Earlier this year, President Obama declared his support for gay marriage, and Attorney General Eric Holder announced the administration no longer would defend the Defense of Marriage Act.

"2012 has already been the watershed year in the history of this movement," says Chad Griffin, president of the Human Rights Campaign. a gay and lesbian advocacy group. "It's so clear where this country's headed on this issue."

The Supreme Court is closely divided, however, with five conservative justices generally holding sway. To continue their momentum, gay-rights groups will need one or more of those justices to uphold the lower court rulings. Organizations opposed to gay marriage don't think that will happen.

The high court's recent rulings in gay rights cases "do not indicate that the court is anywhere near going in a new direction - to require government endorsement of alternative lifestyles," says Andrew Pugno, general counsel for ProtectMarriage, which is challenging the court decisions that threw out Proposition 8. "Recent cases have only said that you cannot criminalize or discriminate, you cannot target homosexuals."

For the court, taking on same-sex marriage will mean a 2012-13 term as controversial as last year's, which was headlined by the 5-4 decision upholding Obama's landmark health care law. Already, the justices have agreed to consider challenges to college affirmative action programs and federal oversight of voting laws in states with a history of racial discrimination.

The gay-rights cases hinge on the Constitution's guarantee of equal protection. Gay-rights groups say the the federal and state laws in question deny that protection to gays and lesbians seeking the same marriage rights as heterosexuals. Those on the other side say there is no constitutional right to same-sex marriage, and states cannot obligate the federal government to bless it under more than 1,100 federal statutes.

Federal district and appeals courts have sided with the laws' opponents, ranging from an 83-year-old lesbian widow in New York to a 50-year-old employee of the 9th Circuit Court of Appeals in California.

Since the Justice Department no longer has its back, the Defense of Marriage Act now is defended by the leadership of the Republican-majority House of Representatives.

"The court will want to take this issue and get it resolved, one way or another," says Paul Clement, a former solicitor general under President George W. Bush, who represents the so-called Bipartisan Legal Advisory Group.

Clement's predecessor as solicitor general, conservative stalwart Theodore Olson, now represents the gay and lesbian plaintiffs fighting California's Proposition 8. He wants the lower court ruling there left alone, thereby legalizing same-sex marriage once again in the nation's largest state and doubling the number of Americans living in states that permit it.

"The question whether the states may discriminate against gay men and lesbians in the provision of marriage licenses," Olson wrote in his brief to the high court, "is the defining civil rights issue of our time."

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