SAN FRANCISCO — Even as same-sex couples across California begin making plans to tie the knot, opponents are redoubling their efforts to make sure wedding bells never again ring for gay couples in the nation's most populous state.

A conservative group said it would ask California's Supreme Court to postpone putting its Thursday decision legalizing gay marriage into effect until after the fall election. That's when voters will likely have a chance to weigh in on a proposed amendment to California's constitution that would bar same-sex couples from getting married.

If the court does not put its ruling on hold, gay marriages could begin in California in as little as 30 days, the time it typically takes for the justices' opinions to become final.

The Republican-dominated court's decision, which cited a 1948 California Supreme Court decision that overturned a ban on interracial marriages, swept away decades of tradition and said there was no legally justifiable reason why the state should withhold the institution of marriage because of a couple's sexual orientation.

The 4-3 opinion written by Chief Justice Ronald George said domestic partnerships that provide many of the rights and benefits of matrimony are not enough.

"In contrast to earlier times, our state now recognizes that an individual's capacity to establish a loving and long-term committed relationship with another person and responsibly to care for and raise children does not depend upon the individual's sexual orientation," George wrote for the majority in ringing language that delighted gay rights activists.

Gay marriage opponents, meanwhile, derided the ruling as an example of judicial overreaching in which the opinions of a few justices trumped the will of Californians.

"The remedy is a constitutional amendment," said Glen Lavy, senior counsel for the Alliance Defense Fund, which is pushing for the stay.

The last time the state's voters were asked to express their views on same-sex marriage at the ballot box was in 2000, the year after the Legislature enacted the first of a series of laws awarding spousal rights to domestic partners.

Proposition 22, which strengthened the state's 1978 one-man, one-woman marriage law with the words "Only marriage between a man and a woman is valid or recognized in California," passed with 61 percent of the vote.

The Supreme Court's ruling Thursday struck down both statutes.

Still, backers of a proposed November ballot measure that would allow Californians to vote on a constitutional amendment banning same-sex marriage said the court's decision would ultimately help their cause.