The proceedings, which are expected to last two to three weeks, involve a challenge to Proposition 8, the gay marriage ban approved by California voters in November 2008.
CBS News correspondent John Blackstone reports Proposition 8 ended five months of legal same sex marriages in California. The trial beginning Monday pits two couples who claim the ban violates their federal constitutional rights to due process and equal treatment, against a voter-won proposition which defines marriage as between a man a woman.
Regardless of the outcome, the case is likely to be appealed to the U.S. Supreme Court, where it ultimately could become a landmark that determines if gay Americans have the right to marry.
CBS News legal analyst Trent Copeland says the "fundamental issue at play is whether or not a proposition - a measure passed by the will of the people - if it violates the federal constitution, which one prevails?"
The judge who will render a decision, Chief U.S. District Judge Vaughn R. Walker, has asked lawyers arguing for and against the ban to present the facts underlying much of the political rhetoric surrounding same-sex marriage. Among the questions Walker plans to entertain are whether sexual orientation can be changed, how legalizing gay marriage affects traditional marriages and the effect on children of being raised by two mothers or two fathers.
"The case is intriguing, exciting and potentially very significant because it addresses multiple important questions that, surprisingly to many, remain open in federal law," said Jennifer Pizer, marriage director for the gay law advocacy group Lambda Legal. "Can the state reserve the esteemed language and status of marriage just for heterosexual couples, and relegate same-sex couples to a lesser status? Are there any adequate public interests to justify reimposing such a caste system for gay people, especially by a majority vote to take a cherished right from a historically mistreated minority?"
The sponsors of Proposition 8, which passed with 52 percent of the vote, won permission to defend the law in court after Gov. Arnold Schwarzenegger and Attorney General Brown refused to. The attorney general and the governor are defendants in the case because of their positions in state government.
Lawyers for the measure's backers plan to argue that because same-sex marriage still is a social experiment, it is wise for states like California to take a wait-and-see approach. Their witnesses will testify that governments historically have sanctioned traditional marriage as a way to promote responsible child-rearing and that this remains a valid justification for limiting marriage to a man and a woman.
The anticipation and tension surrounding the trial were evident over the weekend, when Proposition 8's sponsors asked the U.S. Supreme Court to stop the proceedings from being recorded and broadcast on YouTube. Walker approved such a plan last week, saying the case was appropriate for wide dissemination because it dealt with an issue of wide interest and importance.
Justice Anthony Kennedy, who oversees the federal courts in western states, did not act on the emergency petition Sunday night.
While other courts have wrestled with the constitutional issues raised by prohibiting same-sex marriages - the Supreme Court last took a look at the issue 38 years ago - Walker's court is the first to employ live witnesses in the task. Among those set to testify are the leaders of the Proposition 8 campaign, academic experts from the fields of political science, history, psychology and economics, and the two plaintiff couples - Kristin Perry and Sandra Stier, who live in Berkeley, and Paul Katami and Jeffrey Zarrillo, who live in Los Angeles.
Chad Griffin, a political consultant who helped spearhead the lawsuit, said the four were recruited to represent California couples who say they would get married were it not for Proposition 8 because they lead lives indistinguishable from those of other couples, gay or straight, who have jobs, children and a desire for the social stamp of approval that matrimony affords, Griffin said.
"Our story, I think, is pretty ordinary," said Perry, 45, the title plaintiff in the case registered on legal dockets as Perry v. Schwarzenegger. "We fell in love, we want to get married and we can't. It's pretty simple." The women have been together for almost 10 years and since 2004 have been registered domestic partners, a legal relationship that in California carries most of the benefits and obligations of a full-fledged marriage.
Stier, 47, was married to a man for 12 years. She said the differences between marriage and domestic partnerships, part of what will be debated during the trial, are profound. She and Perry have to take extra legal precautions when they travel to states that do not recognize gay relationships and continually explain to friends and family what a domestic partnership is, Stier said.
"I had that feeling of security that comes with marriage and the assumption of many of the comforts and protections society affords. I can feel the difference in a very personal way," she said. "The word 'partnership' is used for business deals, tennis matches and golf games. It doesn't feel like the appropriate kind of word to describe my relationship with the person I love."