Advocates and opponents of same sex marriage are keenly awaiting a federal appeals court decision due to be published shortly on whether Proposition 8, a measure banning it in California, violates the civil rights of gay and lesbian people.

A three-judge panel of the 9th US circuit court of appeals which has been considering the legality of the said in a statement it planned to release its long-awaited findings on Tuesday lunchtime. The unusual decision to give notice of its findings reflects the immense public interest in the case.

Voters in California passed Proposition 8 in 2008, but it was ruled unconstitutional by federal judge Vaughn Walker in 2010. But the ban has remained in place since then, because the ninth circuit court put a stay on the Walker ruling pending appeals.

However, even if the panel upholds the ruling by Walker, a former chief US district judge, and overturns the ban, same-sex marriages are unlikely to go ahead any time soon.

Backers of Proposition 8 have said they plan to appeal to a larger 9th circuit panel and then to the US supreme court if they lose.

As a result, same sex couples in California, who enjoyed a brief, four-month legal right to marry in 2008, are likely to have to wait longer to find out if it will be restored.

The case has already been subjected to lengthy delays. Arguments about the constitutional implications of the case were heard by the panel more than a year ago.

But it put off a decision in order to seek guidance from the California supreme court on whether the ban's sponsors had the legal authority to challenge the ruling. The state's attorney general and governor had decided not to appeal it.

In November, the California court gave the ballot measure backers the go-ahead, ruling that the state's citizens' initiative process grants sponsors the right to defend such measures in court even if state officials refuse to do so.

The case was further complicated when lawyers for the coalition of conservative religious groups behind the ballot measure tried to have the trial ruling struck down after it emerged that Walker was in a long-term relationship with another man.

They argued he should have revealed his relation before he declared the measure unconstitutional in August 2010.

Walker disclosed he was gay and had a partner of 10 years after he retired from the bench last year.

However, Walker's successor as the chief federal judge in northern California, James Ware, rejected claims that Walker was unqualified to preside over the 13-day trial.

An estimated 18,000 same-sex couples in California wed during the four-month hiatus before Proposition 8 took effect, according to the Williams Institute on Sexual Orientation and the Law, a thinktank based at the University of California, Los Angeles.

"The circumstances in California are unprecedented" Tobias Barrington Wolff, a professor at the University of Pennsylvania Law School, told the Associated Press. "The state supreme court found marriage equality to be a right of the highest order under the state Constitution, and thousands of couples actually exercised that right before a discriminatory initiative took it away"

"The federal courts would do well to focus their attention on those unique circumstances, which would support a ruling that Proposition 8 is unconstitutional while leaving the situation in other states for another day."

California voters passed Proposition 8 with 52% of the vote in November 2008, five months after the supreme court legalised same-sex marriage by striking out laws that had limited marriage to those of opposite genders.

The ballot measures effectively inserted the opposite gender requirement into the state constitution.