LOS ANGELES - Excitement is building as gay couples across the country watch the clock tick down to 5:01 p.m. Pacific Time today.

That's the minute gay marriage becomes legal in the largest state in the union under last month's historic ruling from the California Supreme Court.

"Obviously it's a momentous day," said Upper West Side resident Inga Sarda-Sorensen, 43, who's planning to wed partner Jennie Talley, 54, at a ceremony in Malibu this September.

They are in the throes of planning their 30-guest affair and spent this morning shopping for "elegant wedding pantsuits" online.

"We have friends who have gone to Canada to get married, and that's been a wonderful experience. But for us, it's very import that we're able to get married in our country," Sarda-Sorensen, a spokeswoman for the National Gay and Lesbian Task Force, said. "This is where we live and this is where we born and raised, and that's important to us."

An estimated 12,190 gay couples from New York are expected to travel to California to marry in next three years, a study by the UCLA Williams Institute says.

Kicking things off tonight are two high-profile nuptials linked to the court battles that have revolutionized California's marriage laws.

Robin Tyler and Diane Olson of Los Angeles will marry in Beverly Hills with an early license granted because the women, together 15 years, were original plaintiffs in the suit that lifted the ban on same-sex marriage.

Gay rights pioneers Del Martin, 87, and Phyllis Lyon, 84, will exchange vows for a second time tonight at a 50-guest ceremony in the City Hall office of San Francisco Mayor Gavin Newsom. The couple first exchanged wedding vows in a 2004 challenge of California laws, but the courts voided it.

"It's really just amazing the progress we've made," Lyon told the San Francisco Chronicle.

Thousands more gay couples are expected to obtain marriage licenses across the state starting tomorrow, the first full day the words "Party A" and "Party B" replace "bride" and "groom" on California marriage licenses.

Many couples say they're undeterred by a November ballot initiative that seeks to amend the state constitution and outlaw gay marriage. They say they're heartened by the strong wording of the Supreme Court ruling and support from around the country.

Gov. Paterson, for example, issued an edict last month that state agencies must recognize gay marriage performed legally outside of New York.