The legal fight over same-sex marriage has shifted to Southern California now that a lawsuit filed by a gay couple from suburban Orange County (search) is the only remaining challenge to the federal Defense of Marriage Act (search).

Christopher Hammer and Arthur Smelt plan to be in U.S. District Court on Thursday as their attorney argues that the federal law, as well as California's Proposition 22 (search), are violations of civil rights akin to slavery or denying women the right to vote.

California recognizes only marriages between a man and a woman, and the Defense of Marriage Act allows states to disregard gay marriages performed in other states and foreign countries.

The hearing comes two days after gay couples in Florida decided to drop similar lawsuits.

"Certainly, eyes are going to be focused on this particular case," said Matthew Staver, president of Liberty Counsel, an opponent of gay marriage involved in some 30 cases nationwide.

The only other same-sex marriage case pending in federal court, according to lawyers on both sides of the debate, is one in Nebraska that challenges a state law on same-sex marriages. The judge has not ruled yet in that case.

Hammer and Smelt, both 45, met in 1996 and held a commitment ceremony in their Mission Viejo home a year later. They tried to get a marriage license in Orange County at the time but were turned down.

"I was laughed at," Hammer said.

Last year, as the couple watched news reports of gays and lesbians getting married in San Francisco — ceremonies later halted by a court — they decided to give it another shot. Turned down again, they filed a lawsuit.

Their attorney, Richard C. Gilbert, pursued the case in federal court, even though most cases elsewhere were filed in state courts, where activists believe their chances are better.

"Marriage traditionally has been a state law matter," said Jennifer Pizer, senior counsel with the Lambda Legal Defense and Education Fund, a national gay rights organization.

On Tuesday, three gay couples in Florida dropped their lawsuits challenging the Defense of Marriage Act after a judge dismissed their cases. They decided not to risk appeals that could result in the U.S. Supreme Court setting a precedent by rejecting the cases.

Gilbert, who said his arguments are different from those used in Florida, said he will appeal if he loses before the federal judge in Santa Ana.

"I'll fight all the way to the United States Supreme Court if these plaintiffs are willing to fight," he said.

In Thursday's hearing, Gilbert will go up against lawyers for the U.S. Department of Justice, the California Attorney General's Office and Orange County.

The judge will also hear from two private groups — the Florida-based Liberty Counsel and Arizona-based Alliance Defense Fund — that believe gay marriages undermine traditional marriage.