WASHINGTON — Opponents of gay marriage in California filed an appeal Tuesday asking the US Supreme Court to overturn a federal court decision legalizing same-sex unions.

"The profoundly important question, whether the ancient and vital institution of marriage should be fundamentally redefined to include same-sex couples is currently a matter of great debate in our nation," read the appeal, of which AFP obtained a copy.

The appeal is one of several on the issue of same-sex marriage the Supreme Court will decide whether to review when it resumes on September 24.

"Whether the Constitution requires California to eliminate the most longstanding universal and fundamental of these conditions -- that a marriage consists of a man and woman -- is a question that should be settled by this Court," the appeal added.

Gay marriage has fueled much debate in the US, especially after Democratic President Barack Obama came out in favor of same-sex marriage in an interview in May.

Same-sex marriage was briefly authorized in California, before the adoption of Proposition 8 -- commonly known as Prop 8 -- in a state-wide vote in 2008. The proposition entered into the state constitution that marriage is between a man and a woman.

On February 21 this year, a federal appeals court in California ruled Prop 8 unconstitutional, in a decision that the most recent appeal aims to overturn.

Analysts say the nine Supreme Court justices are more likely to take on cases related to the Defense of Marriage Act (DOMA) -- the subject of litigation in the northeastern state of Massachusetts.

DOMA stipulates marriage is a legal union between a man and a woman. The law prevents couples in same-sex units from obtaining the same federal benefits -- including inheritance rights and tax deductions -- accorded to their heterosexual counterparts.

Analysts also say judges are unlikely to rule in favor of the national legalization of gay marriage, but will more likely address same-sex unions in states where it is already permitted.

Legal marriage between two men or two women is not recognized by the US federal government but is now allowed in six of the 50 US states and in the federal capital city, Washington.