A federal appeals court is expected to decide Tuesday whether California's ban on same-sex marriage violates the federal Constitution, a ruling that could reach the U.S. Supreme Court next year.

A three-judge panel of the 9th U.S. Circuit Court of Appeals announced Monday that it would release its long-awaited decision by 10 a.m. PST.

The panel, which includes two Democratic appointees and one Republican, will decide whether Proposition 8, the same-sex marriage ban passed by voters in 2008, violates equal protection and due process guarantees of the U.S. Constitution.

Two same-sex couples challenged Proposition 8 just days before the California Supreme Court upheld it as a valid state constitutional amendment. The suit led to an historic federal trial that examined the nature of sexual orientation, the history of marriage, and discrimination against gays and lesbians.

Retired Chief U.S. District Judge Vaughn R. Walker presided over the trial and ruled against Proposition 8 in 2010, but the 9th Circuit issued a stay to put his ruling on hold pending appeals.

The stay could remain in place even if the panel rules against Proposition 8. If the panel lifts the stay, backers of Proposition 8 could ask the U.S. Supreme Court to reinstate it.

The losing party can appeal the ruling to a larger panel of the 9th Circuit, which would delay U.S. Supreme Court review for many months or longer, or go directly to the high court. The sponsors of Proposition 8, ProtectMarriage, have said they were eager to get to the high court as soon as possible.

"Either side that loses would want to read the opinion and look at the vote count before making an en banc decision," said University of California, Irvine Law School Dean Erwin Chemerinsky.

During oral arguments more than a year ago, the panel appeared to be leaning toward ruling against Proposition 8 but expressed concern about procedural matters.

The panel since then has been asked to decide, in addition to the constitutional questions, whether Walker's ruling should be overturned on the grounds that he failed to disclose he was in a long-term same-sex relationship.

The court's decision would have no immediate effect on other states within the 9th Circuit, lawyers said Monday. Even if Proposition 8 is struck down and the stay lifted, marriage bans in other states would probably continue until challenged or until state officials refused to recognize them, attorneys said.

The judges on the Proposition 8 panel are Stephen Reinhardt, an appointee of former President Jimmy Carter; Michael Daly Hawkins, an appointee of former President Bill Clinton; and N. Randy Smith, appointed by former President George W. Bush.