The city of San Francisco, which galvanized a national debate over same-sex weddings when it allowed gay couples to marry in 2004, asked a California appeals court to reject as unconstitutional a state law banning the unions.

California’s domestic partnership law, which doesn’t give same-sex couples all of the same rights as heterosexual married couples, created a separate system that denies gays and lesbians the social recognition that comes with marriage, Therese Stewart, chief deputy city attorney, said today at a hearing in San Francisco. She asked a three-judge appeals panel to uphold a lower court ruling that struck down the ban.

“It tells the world that California believes these relationships are as important as any other couples,” Mr. Stewart said. Massachusetts is the only American state to allow gay marriages. On July 6, courts in New York and Georgia rejected legal recognition of same-sex weddings while appeals of gay marriage bans in New Jersey and Washington are pending.

Last year’s ruling rejecting California’s ban followed lawsuits over San Francisco’s decision to issue marriage licenses to 4,000 couples. Superior Court Judge Richard Kramer said there is “no rational basis” for California to exclude same-sex couples. He put his ruling on hold pending appeals.

The appeals court opinion is expected in about 90 days. The appeals court’s eventual decision can be appealed to the state supreme court.