The Supreme Court released two major decisions expanding gay rights across the country on Wednesday as hordes of cheering demonstrators greeted the news outside. The justices struck down a federal law barring the recognition of same-sex marriage in a split decision, ruling that the law violates the rights of gays and lesbians and intrudes into states' rights to define and regulate marriage. The court also dismissed a case involving California's gay marriage ban, ruling that supporters of the ban did not have the legal standing, or right, to appeal a lower court's decision striking down Proposition 8 as discriminatory.

The decision clears the way for gay marriage to again be legal in the nation's most populous state, even though the justices did not address the broader legal argument that gay people have a fundamental right to marriage.

The twin decisions throw the fight over gay marriage back to the states, because the court ruled the federal government must recognize the unions if states sanction them, but did not curtail states' rights to ban gay marriage if they choose.

Justice Anthony Kennedy, the court's conservative-leaning swing vote with a legal history of supporting gay rights, joined his liberal colleagues in the DOMA decision, which will dramatically expand the rights of married gay couples in the country to access more than 1,000 federal benefits and responsibilities of marriage previously denied them.

"The avowed purpose and practical effect of the law here in question are to impose a disadvantage, a separate status, and so a stigma upon all who enter into same-sex marriages made lawful by the unquestioned authority of the States," Kennedy wrote of DOMA. He concluded that states must be allowed by the federal government to confer "dignity" on same-sex couples if they choose to legalize gay marriage. DOMA "undermines" same-sex marriages in visible ways and "tells those couples, and all the world, that their otherwise valid marriages are unworthy of federal recognition."

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Eighty-three-year-old New Yorker Edith Windsor brought the DOMA suit after she was made to pay more than $363,000 in estate taxes when her same-sex spouse died. If the federal government had recognized her marriage, Windsor would not have owed the sum. She argued that the government has no rational reason to exclude her marriage (she and her late partner, Thea Spyer, had been married since 2007, and together for more than four decades) from the benefits and obligations other married couples receive.

DOMA, which was signed into law by President Bill Clinton in 1996, prevented the government from granting marriage benefits in more than 1,000 federal statutes to same-sex married couples in the 12 states and District of Columbia that allow gay marriage. Clinton, who disavowed the law earlier this year, released a statement congratulating Windsor on her victory. Attorney General Eric Holder said the Justice Department would "work expeditiously" to implement the decision, and called it a "triumph for equal protection under the law for all Americans."

With this decision, Kennedy furthers his reputation as a defender of gay rights from the bench. He wrote two of the most important Supreme Court decisions involving, and ultimately affirming, gay rights: Lawrence v. Texas (2003) and Romer v. Evans (1996). In Romer, Kennedy struck down Colorado's constitutional amendment banning localities from passing anti-discrimination laws protecting gays and lesbians. In Lawrence, Kennedy invalidated state anti-sodomy laws, ruling that gay people have a right to engage in sexual behavior in their own homes free from the fear of punishment.

Legal experts said the DOMA decision lays the foundation for a future Supreme Court ruling that could find a broader right for same-sex couples to marry.

The decisions mark the first time the highest court has waded into the issue of same-sex marriage. Just 40 years ago, the Supreme Court tersely refused to hear a case brought by a gay couple who wanted to get married in Minnesota, writing that their claim raised no significant legal issue. At the time, legal opinions often treated homosexuality as criminal, sexually deviant behavior rather than involuntary sexual orientation.

Since then, public opinion has changed dramatically on gay people and same-sex marriage, with a majority of Americans only just recently saying they support gay unions. Now, 12 states representing about 18 percent of the U.S. population allow same-sex marriage. With California, the percentage of people living in gay marriage states shoots up to 30.

With the Proposition 8 decision, the Supreme Court refused to wade into the constitutional issues surrounding the California gay marriage case, dismissing the Proposition 8 argument on procedural grounds. The legal dodge means a lower court's ruling making same-sex marriage legal in California will most likely stand, opening the door to marriage to gays and lesbians in the country's most populous state without directly ruling on whether gay people have a constitutional right to marriage.

California voters passed Proposition 8 to ban same-sex marriage in 2008, after 18,000 same-sex couples had already tied the knot under a state Supreme Court decision legalizing gay marriage. A same-sex married couple with children, Kris Perry and Sandy Stier, sued the state of California when their 6-month-old marriage was invalidated by the ballot initiative. They argued that Proposition 8 discriminated against them and their union based only on their sexual orientation, and that the state had no rational reason for denying them the right to marry. Two lower courts ruled in their favor, and then-California Gov. Arnold Schwarzenegger announced he would no longer defend Proposition 8 in court, leaving a coalition of Proposition 8 supporters led by a former state legislator to take up its defense.

Chief Justice John Roberts joined with Antonin Scalia, Ruth Bader Ginsburg, Stephen Breyer and Elena Kagan to rule the defenders of Proposition 8 did not have the standing to defend the ban in court. The unlikely coalition of liberals and conservatives argued that the Proposition 8 supporters could not prove they were directly injured by the lower court's decision to overturn the ban and allow gay people to marry.

Same-sex marriage will most likely not be immediately legal in California, because the Ninth Circuit has several weeks to confirm the court's decision. California officials have asked county clerks offices to prepare to issue marriage licenses to same-sex couples as soon as the decision is confirmed.

The Proposition 8 case was argued by two high-profile lawyers, Ted Olson and David Boies, who previously faced off against each other in Bush v. Gore. Olson, a conservative and Bush's former solicitor general, and Boies, a liberal, have cast gay marriage as the civil rights issue of our time.

Boies said on the steps of the Supreme Court on Wednesday that the court had shown gay marriage does not harm society. "Today the United States Supreme Court said as much," Boies said. "They cannot point to anything that harms them because these two love each other.”

President Barack Obama also reportedly called Chad Griffin, the president of the Human Rights Campaign gay rights group, to congratulate him on the legal victory. "We're proud of you guys, and we're proud to have this in California," the president said, according to audio on MSNBC.

"The laws of our land are catching up to the fundamental truth that millions of Americans hold in our hearts: When all Americans are treated as equal, no matter who they are or whom they love, we are all more free," the president said in a statement.

Olson made the argument that gay marriage should be a conservative cause in a recent interview with NPR. "If you are a conservative, how could you be against a relationship in which people who love one another want to publicly state their vows ... and engage in a household in which they are committed to one another and become part of the community and accepted like other people?" he asked.

The Bipartisan Legal Advisory Group, a coalition of mostly Republican House lawmakers, defended DOMA after the Obama administration announced it believed the law was unconstitutional in 2011. (Roberts criticized the president for this move during oral arguments in the case, saying the president lacked “the courage of his convictions” in continuing to enforce the law but no longer defending it in court.)

"While I am obviously disappointed in the ruling, it is always critical that we protect our system of checks and balances," House Speaker John Boehner, R-Ohio, said in a statement. "A robust national debate over marriage will continue in the public square, and it is my hope that states will define marriage as the union between one man and one woman."

Faith and Freedom Coalition Chairman Ralph Reed said in a statement that his political advocacy group would push for federal legislation to try to restore DOMA. He called the decision "an Orwellian act of judicial fiat."

—Rachel Rose Hartman contributed to this report.