SAN FRANCISCO — In nearly two years since John Lewis and Stuart Gaffney took part in this city’s same-sex marriage rebellion, they have filed three rounds of tax returns, buried a mother, vacationed in Europe, and attended five weddings — four involving both a bride and a groom.

These are the typical joys, sorrows, and rituals of couples who have been together for nearly two decades.Yet for Messrs. Lewis and Gaffney, one of 4,037 pairs whose San Francisco-issued marriage licenses were invalidated by the California Supreme Court, daily domesticity also brings reminders of the legal rights they do not have and are suing to secure.

“We took a vow at San Francisco City Hall to be together for better or worse,” said Mr. Gaffney, 43. “It’s hard because while we wait, we wait in a separate and unequal status.”

A state appeals court in San Francisco today will consider whether a trial judge erred in declaring the state’s existing marriage laws unconstitutional.

The First District Court of Appeal is scheduled to hear six hours of arguments in as many related cases — four of them filed by the city and lawyers for 20 couples seeking the right to wed, and two brought by groups that want to maintain the status quo barring same-sex unions.

Although any ruling is expected to be appealed to the state Supreme Court, advocates on both sides say the stakes remain high at the intermediate court. New York’s highest court upheld that state’s one man-one woman marriage laws on Thursday, shifting the gay rights movement’s focus to other jurisdictions that might join Massachusetts in legalizing gay marriage.

High courts in New Jersey and Washington state are already deliberating cases brought by same-sex couples. But it is California, home to more same-sex couples than any other state, where a ruling could have the most impact.

“California is the most diverse state in the country, and the gay community has achieved a kind of visibility and integration here that is unlike any state,” a lawyer with the Lambda Legal Defense and Education Fund who is representing gay couples in both California and Washington, Jennifer Pizer, said.

The appeals that will be heard today were brought by California’s attorney general and two groups opposed to gay marriage. They followed San Francisco Superior Court Judge Richard Kramer’s March 2005 ruling that the state’s existing marriage laws violated the civil rights of gays and lesbians by denying them “the basic human right to marry a person of one’s choice” and by discriminating on the basis of gender and sexual orientation.