Beck Diefenbach / Reuters file Gay marriage advocates cheer during a rally outside a federal courthouse in San Francisco moments before hearing that judges had struck down Proposition 8, which bans same-sex marriage, on Feb. 7, 2012.

Backers of California's Proposition 8, intended to ban same-sex marriage in the state, asked the U.S. Supreme Court on Tuesday to take up their appeal after two lower federal courts found the measure unconstitutional.

The justices now face two gay rights issues: the Prop 8 appeal and two challenges to the federal Defense of Marriage Act.

Voters in California approved Prop 8 in 2008, less than six months after the state’s Supreme Court approved same-sex marriage. The measure was immediately challenged.

A federal judge declared it unconstitutional in 2010, and a three-judge panel of the 9th U.S. Circuit Court of Appeals ruled 2-1 in February that the ban discriminated against gays and lesbians. The full circuit declined to hear the appeal from Prop 8 supporters, though its ruling remains on hold until all legal avenues have been exhausted.

In urging the Supreme Court to hear their appeal, backers of the measure – which includes that Alliance Defending Freedom, a legal ministry -- said the nation was in the midst of a public debate about "the profoundly important question” of “whether the ancient and vital institution of marriage should be fundamentally redefined to include same-sex couples."

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Proponents of Prop 8 stepped in to lead the court battle after California officials concluded the ban was unconstitutional and declined to defend it.

The federal appeals court wrongly concluded, the Prop 8 backers said in their petition Tuesday, that because California's domestic partnership law already gave same-sex couples the same legal rights that married couples have, all the measure did was take away their legal right to get marriage licenses.

Such a distinction, the appeals court determined, had no effect other than to lessen the status and human dignity of gays and lesbians. The court also found that Prop 8 unconstitutionally took away a fundamental right that the state had previously guaranteed.

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"This reasoning calls into immediate question the marriage laws of Hawaii, Nevada, and Oregon, which extend to same-sex couples the incidents but not the designation of marriage," lawyers for the Prop 8 supporters argued in their Supreme Court filing.

The appeals court ruling "threatens to short-circuit further democratic deliberation regarding official recognition of same-sex marriage," they said.

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Separately, both the Obama administration and House Republicans are urging the Supreme Court to decide the constitutionality of a provision in the federal Defense of Marriage Act, passed in 1996 and signed into law by former President Bill Clinton.

DOMA, as the law is known, prevents the federal government from recognizing same-sex marriage -- even in states where it is legal -- thereby denying various benefits given to heterosexual couples.

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The Obama administration had stopped defending the law, concluding it was unconstitutional. It recently asked the Supreme Court to take up two of the DOMA cases – one originating in Massachusetts, the other in California -- after appeals courts struck the law down.

Neither case sought for justices to decide the fundamental question of whether the Constitution guarantees same-sex couples the right to marry. No Supreme Court action on whether to take up any of the cases, or all of them, is expected until the fall.

No same-sex marriages have been performed in California since Prop 8 was passed by voters.

Equality California, a LGBT advocacy group, said there was no need for the Supreme Court to review the case because the decision to strike down Prop 8 “rested on solid constitutional principles.”

"Two federal courts in this case have affirmed what we know to be true -- that Proposition 8 seriously infringes on the guarantee of equal protection and serves no legitimate state interest,” the group’s spokeswoman, Rebekah Orr, said in an email. “We look forward to a day in the near future when all loving, committed couples will have the freedom to commit their lives to one another in marriage and enjoy the security and protection that only marriage can provide."

NBC News’ Miranda Leitsinger contributed to this report.

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