SAN FRANCISCO - Even as same-sex couples across California make plans to tie the knot, foes of gay marriage are redoubling efforts to make sure those wedding bells never ring.

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 is when voters will likely have a chance to weigh in on a proposed amendment to the state constitution to bar same-sex marriage.

If the court does not put its ruling on hold, gay marriages could begin in California in as few 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 overturning a ban on interracial marriages, said there was no legally justifiable reason to 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 were not enough.

Gay-marriage foes derided the ruling as an example of judicial overreaching.

"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 state voters were asked to express their views on same-sex marriage at the ballot box was in 2000, the year after lawmakers 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 that statute.

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

The ruling "is not the way a democracy is supposed to handle these sorts of heartfelt, divisive issues," said Brian Brown of the National Organization for Marriage, a group backing the anti-gay-marriage campaign. "I do think it will activate and energize Californians."

Twenty-six states have approved constitutional amendments banning same-sex marriage. A proposed constitutional ban on gay marriage was tabled in the Pennsylvania Senate this month.

In the last few years, courts in New York, Maryland and Washington state have refused to allow gay marriage.

New Jersey's highest court gave state lawmakers the option of establishing civil unions as an alternative.

Massachusetts is the only other state to legalize gay marriage; it did so in 2004.

The California ruling is considered monumental because of the state's population - 38 million out of a U.S. population of 302 million - and its historical role as the vanguard of many social and cultural changes that have swept the country since World War II. The state has 108,734 same-sex households, according to 2006 census figures.

The case was set in motion in 2004 when San Francisco Mayor Gavin Newsom threw open City Hall to gay couples to get married in a challenge to California law. Four thousand wed before the Supreme Court halted the practice after a month. Two dozen gay couples then sued, along with the city and gay-rights organizations.