The justices issued two 5-4 rulings in their final session of the term. One decision wiped away part of a federal anti-gay marriage law that has kept legally married same-sex couples from receiving tax, health and pension benefits.
The other was a technical legal ruling that said nothing at all about same-sex marriage, but left in place a trial court's declaration that California's Proposition 8 is unconstitutional. That outcome probably will allow state officials to order the resumption of same-sex weddings in the nation's most populous state in about a month.
In a sign that neither victory was complete, the high court said nothing about the validity of gay marriage bans in California and roughly three dozen other states. And a separate provision of the federal marriage law that allows a state to not recognize a same-sex union from elsewhere remains in place.
President Barack Obama telephoned his congratulations to the plaintiffs in the California case from Air Force One en route to Africa.
The ruling in that case was not along ideological lines. Chief Justice John Roberts wrote the majority opinion, joined by Justices Ruth Bader Ginsburg, Stephen Breyer, Elena Kagan and Antonin Scalia.
"We have no authority to decide this case on the merits, and neither did the 9th Circuit," Roberts said, referring to the federal appeals court that also struck down Proposition 8.
In the case involving the federal Defense of Marriage Act, Justice Anthony Kennedy wrote the majority opinion, joined by the court's liberal justices.
"Under DOMA, same-sex married couples have their lives burdened, by reason of government decree, in visible and public ways," Kennedy said.
"DOMA's principal effect is to identify a subset of state-sanctioned marriages and make them unequal," he said.
Some in the crowd outside the court hugged and others jumped up and down just after 10 a.m. EDT Wednesday when the DOMA decision was announced. Many people were on their cell phones monitoring Twitter, news sites and blogs for word of the decision. And there were cheers as runners came down the steps with the decision in hand and turned them over to reporters who quickly flipped through the decisions.
Chants of "Thank you" and "USA" came from the crowd as plaintiffs in the cases descended the court's marbled steps. Most of those in the crowd appeared to support gay marriage, although there was at least one man who held a sign promoting marriage as between a man and a woman.
Kennedy was joined in the DOMA decision by the court's four liberal justices.
Chief Justice John Roberts, Justices Samuel Alito and Clarence Thomas, and Scalia dissented.
Same-sex marriage has been adopted by 12 states and the District of Columbia. Another 18,000 couples were married in California during a brief period when same-sex unions were legal there.
The outcome is clear for people who were married and live in states that allow same-sex marriage. They now are eligible for federal benefits.
The picture is more complicated for same-sex couples who traveled to another state to get married, or who have moved from a gay marriage state since being wed.
Their eligibility depends on the benefits they are seeking. For instance, immigration law focuses on where people were married, not where they live. But eligibility for Social Security survivor benefits basically depends on where a couple is living when a spouse dies.
The rulings came 10 years to the day after the court's Lawrence v. Texas decision that struck down state bans on gay sex. In his dissent at the time, Scalia predicted the ruling would lead to same-sex marriage
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