* Court to review U.S. law denying federal benefits
* Will also review California gay marriage ban
* More than 30 states ban same-sex marriage
By Terry Baynes
WASHINGTON, Dec 7 (Reuters) - The U.S. Supreme Court stepped into the gay marriage debate for the first time on Friday by agreeing to review two challenges to federal and state laws that define marriage as a union between a man and a woman.
The high court agreed to review a case against a federal law that denies married same-sex couples the federal benefits heterosexual couples receive. It also took up a challenge to California's ban on gay marriage, known as Proposition 8, which voters narrowly approved in 2008.
Same-sex marriage is a politically charged issue in a country where 31 of the 50 states have passed constitutional amendments banning it, while Washington, D.C., and nine states have legalized it, three of them on Election Day last month.
Yet even where it is legal, married same-sex couples do not qualify for a host of federal benefits because the 1996 Defense of Marriage Act, or DOMA, passed by Congress, only recognizes marriages between a man and a woman.
Gays and lesbians married under state laws have filed suits challenging their denial of such benefits as Social Security survivor payments and the right to file joint federal tax returns. They argue the provision, known as Section 3, violates equal protection provisions of the U.S. Constitution.
Meeting in private on Friday at their last weekly conference before the court's holiday recess, the justices considered requests to review seven cases dealing with same-sex relationships. Five of them were challenges to the federal marriage law, one to California's gay marriage ban and another to an Arizona law against domestic partner benefits.
The court had been widely expected to take up at least one of the challenges to the federal marriage law, given that two federal appeals courts had found the law unconstitutional. Less clear was what the court would do with the California gay marriage ban.
"Taking both a states' rights case like Prop 8, and a case involving Congress's authority in the DOMA ... suggests that the court is ready to take on the entire issue, not just piecemeal it," said Andrew Pugno, a lawyer for the individuals defending California's gay marriage ban.
DEFENSE OF MARRIAGE ACT
In an "orders list" released after their meeting, the court granted the appeal of Edith Windsor, an 83-year-old lesbian who challenged her denial of federal tax benefits under the Defense of Marriage Act.
Windsor's wife, Thea Clara Spyer, died in 2007, but because the same-sex marriage was not recognized under federal law, Windsor had to pay more than $363,000 in federal estate taxes on assets she inherited from Spyer, according to her lawsuit.
Federal courts of appeal in New York and Boston had found the provision that denies federal recognition and benefits to married same-sex couples unconstitutional.
Democratic President Barack Obama's administration said last year it viewed the law as unconstitutional and would no longer defend it in court. A group appointed by the Republican majority in the U.S. House of Representatives has backed the law, asking the justices to uphold it.
In its order on Friday, the Supreme Court said it wanted to consider whether the congressional group had a right to defend the law, given the Obama administration's conclusion that the law is unconstitutional.
Both sides in the debate welcomed the court's decision to take up the issue.
Civil rights activists, while most focused on state-by-state efforts to legalize same-sex marriage, say it is another breakthrough in their bid for equal rights.
"It is time for the Supreme Court to strike down this unconstitutional statute once and for all," said Donna Lieberman, executive director of the New York Civil Liberties Union, which represents Windsor.
Opponents hope the justices will reverse lower-court rulings and uphold what they regard as U.S. traditional social policy.
"We believe the U.S. Supreme Court will overturn this exercise of judicial activism and stop federal judges from legislating from the bench on the definition of marriage," said John Eastman of the National Organization for Marriage.
If the court invalidates the law, states might still be allowed to legalize or deny same-sex marriages on their own terms.
Another section of the law, which is not being challenged, says that states do not have to give legal status to same-sex marriages performed in other states that permit such unions.
Less expected was the court's decision to review California's ban on same-sex marriage. The California case, Hollingsworth v. Perry, had sought marriage equality for gays and lesbians under the U.S. Constitution.
The 9th Circuit in February found the gay marriage ban unconstitutional. But it ruled narrowly in a way that only affected California and not the rest of the country, finding that the state could not take away the right to same-sex marriage after previously allowing it.
No other state that allowed gay marriage has later banned it.
The court could follow the 9th Circuit's decision and also rule narrowly, allowing same-sex marriage only in California but not the rest of the country. Or it could recognize a right to marriage equality.
In its order list, the court said it wanted to consider whether the gay marriage opponents in the case had standing to defend the law.
If the court finds they don't have a right to defend the law, then gay marriage would become legal in California. But in doing so, the court would not address the broader constitutional rights at stake.
"On the one hand we want our clients and citizens of California to have marriage equality immediately. On the other hand, this is an ideal case for the Supreme Court to decide this critical civil rights issue," said David Boies, a lawyer for the gay marriage advocates.
Lawyers for Indiana and 14 other states had filed a brief in support of Proposition 8, urging the justices to reverse the 9th Circuit's decision and uphold the law, which they say promotes responsible procreation and the ideal family life for children.
California's Attorney General Kamala Harris welcomed the court's decision to consider the case.
"Today's decision by the U.S. Supreme Court to consider marriage equality takes our nation one step closer to realizing the American ideal of equal protection under the law for all people," Harris said in a statement.
The Supreme Court took no action on an appeal from the state of Arizona, asking the court to revive a state law version of DOMA. The Arizona law, which the 9th Circuit invalidated, eliminated domestic partner healthcare benefits for gay and lesbian state employees.
Same-sex couples in Arizona cannot marry, under that state's constitutional ban passed in 2008.