Gay rights advocates sued to overturn the ban four years ago after the court halted a monthslong same-sex wedding spree that saw thousands of couples marry at City Hall.

The justices were scheduled to hear three hours of arguments in six cases.

"I think I speak for everybody when I say that this has been a long time coming and a day that has been eagerly anticipated," said City Attorney Dennis Herrera, who is representing the city in a lawsuit supporting gay marriage.

The cases were filed after the court stopped the same-sex marriages in the winter of 2004. More than 4,000 couples exchanged vows at the direction of Mayor Gavin Newsom months before gay marriage became legal in Massachusetts, although the high court ultimately voided the unions.

In briefs submitted to the court, same-sex marriage supporters argued that California's Constitution leaves no room for denying gays and lesbians the right to wed.

They say that while the state is one of a handful where gay couples are entitled to most of the same legal rights as married spouses, the institution of marriage is too important to allow for alternatives that are by definition inferior.

"We're very hopeful that California history will stay true today and we'll see the constitution vindicated for the thousands of families in California who depend on our equal place under law," said Jennifer Pizer, a lawyer with the Lambda Legal Defense and Education Fund who is representing gay couples.

The state and same-sex marriage opponents, however, maintain that limiting marriage to members of the opposite sex is reasonable — not only to uphold tradition but because California voters approved a ballot initiative eight years ago bolstering the gay-marriage ban that was in place at the time. To overturn that law, they say, would abrogate the rights of all Californians.