The Justice Department is set to urge the Supreme Court to uphold a lower-court ruling and block states from banning same-sex marriage, Attorney General Eric Holder said.
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The nation's top law enforcement official's remarks come just days after Utah officials announced they will ask the Supreme Court to overrule a lower court that concluded gay couples can legally marry in the state.
Last month, a federal appeals court ruled that a state ban on gay marriage, approved by Utah voters in 2004, was unconstitutional, finding that states cannot keep two people from marrying simply because they are of the same sex.
Now the state of Utah is asking the Supreme Court to weigh in, as several other federal appeals courts across the nation consider similar cases that could make their way to the Supreme Court.
If the Supreme Court agrees to hear any of those cases, the Justice Department will file a brief with the court that "will be in support of same-sex marriage," Holder said in a rare interview, sitting down with ABC News' Pierre Thomas.
Holder said the brief would be "consistent with the actions that we have taken over the past couple of years." The Justice Department has refused to defend the Defense of Marriage Act, which defines marriage as between a man and a woman, and its legal efforts to extend federal benefits to same-sex couples have been successful.
Those efforts, Holder said, were "vindicated by the Supreme Court," which ruled last year that same-sex couples must receive the same federal benefits as other married people. That ruling in the so-called "Windsor decision," however, did not specifically address whether gay marriage is a constitutional right.
The Supreme Court could rule on that question if it takes up Utah's appeal or any of the similar cases.
Holder said he believes banning same-sex marriage is unconstitutional, and he's confident the nation's highest court will agree.
"I think a lot of these measures that ultimately will come before the court will not survive a heightened scrutiny examination," he said.
Holder recently called the struggle for gay rights "a defining civil rights challenge of our time," adding that the gay and lesbian community is waiting for an "unequivocal declaration that separate is inherently unequal."
The Associated Press contributed to this report.
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