On the other side of the issue, advocates for same-sex unions said the court could easily decide in favor of gay marriage in California without issuing a sweeping national ruling to overturn every state prohibition on marriage.
In striking down Proposition 8, the 9th U.S. Circuit Court of Appeals crafted a narrow ruling that said because gay Californians already had been given the right to marry, the state could not later take it away. The ruling studiously avoided overarching pronouncements.
"I think the court can easily affirm the 9th Circuit's decision and leave for a later day whether broader bans on marriage are unconstitutional as well," said James Esseks of the American Civil Liberties Union.
The other issue the high court will take on involves a provision of the Defense of Marriage Act, known by its acronym DOMA, which defines marriage as between a man and a woman for the purpose of deciding who can receive a range of federal benefits.
Four federal district courts and two appeals courts struck down the provision. Last year, the Obama administration abandoned its defense of the law, but continues to enforce it. House Republicans are now defending DOMA in the courts.
The justices chose for their review the case of 83-year-old Edith Windsor, who sued to challenge a $363,000 federal estate tax bill after her partner of 44 years died in 2009.
Windsor, who goes by Edie, married Thea Spyer in 2007 after doctors told them that Spyer would not live much longer. She suffered from multiple sclerosis for many years. Spyer left everything she had to Windsor.
There is no dispute that if Windsor had been married to a man, her estate tax bill would have been zero.
The U.S. 2nd Circuit Court of Appeals in New York agreed with a district judge that the provision of DOMA deprived Windsor of the constitutional guarantee of equal protection of the law.
In both cases, the justices have given themselves a technical way out, involving the legal issue of whether the parties have the required legal standing to bring their challenges, which would allow them to duck all the significant issues raised by opponents and supporters of gay marriage.
The cases are Hollingsworth v. Perry, 12-144, and U.S. v. Windsor, 12-307.
Associated Press writer David Crary in New York contributed to this report.