By Pete Williams, Justice Correspondent, NBC News
The Justice Department Thursday urged the US Supreme Court to uphold same-sex marriage in California and went even further, suggesting it is unconstitutional to block gay couples from getting married in half a dozen other states.
States violate the Constitution, the administration argued, if they offer civil unions to gay couples but deny them the right to marry.
While that position clearly applies to the legal dispute in California, it would also apply to at least seven other states -- Delaware, Hawaii Illinois, Nevada, New Jersey, Oregon, and Rhode Island. Each offers civil unions but not same-sex marriage.
And while the administration takes no position in its brief beyond those states, its reasoning would have even broader implications.
If the administration's legal theory were ultimately accepted, no state could, under constitutional guarantees against discrimination, deny same sex couples the right to marry.
After first suggesting it would not get involved in the California case, the Obama administration late Thursday filed a friend-of-the-court brief in support of the two gay couples who launched the fight over the issue four years ago.
In a statement, Attorney General Eric Holder said, "In our filing today in Hollingsworth v. Perry, the government seeks to vindicate the defining constitutional ideal of equal treatment under the law ... The issues before the Supreme Court in this case and the Defense of Marriage Act case are not just important to the tens of thousands Americans who are being denied equal benefits and rights under our laws, but to our Nation as a whole."
Related: 100 Republicans sign brief to the Supreme Court arguing that gays and lesbians should be allowed to legally wed
Supreme Court of the United States
The Supreme Court hears oral argument in late March to decide the fate of Proposition 8, an amendment to the state constitution approved by 52 percent of California voters in 2008. It banned same-sex marriages in the state and went into effect after 18,000 gay couples were legally married earlier that year.
A federal judge declared the ban unconstitutional, and a federal appeals court last year upheld that ruling, though on narrower grounds that apply only to California. In December, the Supreme Court agreed to take up the issue.
The Justice Department is not directly involved in the case, because the gay couples that brought the lawsuit are challenging a state restriction, not a federal one. But each side had urged the government to file a brief in support of its position.
After voters approved the measure stopping same-sex marriage, state officials in California declined to defend it in court. That defense has been carried on by the original proponents of Prop 8.
The Obama administration last year signaled it would stay on the sidelines. In May, when President Obama first said that "same-sex couples should be able to get married," he added that it was not a matter for the federal government.
"This is an issue that is going to be worked out at the local level because historically this has not been a federal issue. Different states are coming to different conclusions," he said in an interview with ABC News.
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But he appeared to express a different view in January, urging legal equality for same-sex couples during his inaugural address.
"Our journey is not complete until our gay brothers and sisters are treated like anyone else under the law, for if we are truly created equal, then surely the love we commit to one another must be equal as well," he said.
In a separate case the administration is urging the Supreme Court to strike down the Defense of Marriage Act, known as DOMA, a law passed by Congress in 1996 that prohibits federal agencies from recognizing same-sex marriages in states where they are legal. As a result, married gay couples are denied over 1,000 federal benefits available to traditional couples.
"The law denies to tens of thousands of same-sex couples who are legally married under state law an array of important federal benefits that are available to legally married opposite-sex couples," Solicitor General Verrelli wrote last week in urging the court to overturn DOMA.
The law is unconstitutional, he said, "because this discrimination cannot be justified as substantially furthering any important governmental interest."
Nine states currently permit same-sex couples to marry -- Connecticut, Iowa, Maine, Maryland, Massachusetts, New Hampshire, New York, Vermont, and Washington. It is also permitted in Washington, D.C.