“It’s going to be the largest, most expensive and most hard fought L.G.B.T. ballot measure in the history of the country,” said Geoff Kors, executive director of Equality California, which works on behalf of lesbian, gay, bisexual and transgendered people. Both sides say they expect to spend $10 million to $20 million on the campaign, which will officially begin when the secretary of state puts the amendment on the ballot, pending spot inspections of more than a million signatures turned in by groups opposing same-sex marriage.
The amendment would insert 14 words into the California Constitution — “Only marriage between a man and a woman is valid and recognized in California” — a phrase tested with focus groups months before the court’s decision.
Advocates for same-sex marriage have also been planning for this fight well before Thursday, forming campaign committees as early as 2003, when an initial effort to change the Constitution began, but failed.
“We didn’t even have to ask what the next step is,” said Kate Kendell, the executive director of the National Center for Lesbian Rights. “We are in full campaign mode. We need money. We need volunteers. We need to begin mobilizing to protect this incredible decision.”
The latest effort to ban same-sex marriage began in earnest in January, when petitioners fanned out across the state with the help of a variety of national groups, including Concerned Women for America and the Family Research Council, both based in Washington. All told, a coalition of groups called Protect Marriage had spent some $1.8 million on the campaign through the end of March, according to state election documents, though much phone and foot work was done by volunteers from churches and other groups...
Thursday’s ruling, which becomes effective after 30 days, would make California the second state to allow same-sex marriages, after Massachusetts.
Constitutional amendments like the one proposed here are preferred by some opponents to same-sex marriage because they are less likely to be overturned by the courts, said David Masci, a senior research fellow at the Pew Forum on Religion and Public Life. And they have been remarkably popular. Voters have approved a ban in 27 of the 28 states that have taken up the issue, Mr. Masci said. Arizona defeated an initiative in 2006.
“There is a concern especially among conservatives that so-called activist judges will see a constitutional right to same-sex marriage,” Mr. Masci said. “Constitutional amendments are seen as a way of stopping that from happening.”
Groups opposed to same-sex marriage say they see several advantages in California, including the somewhat low bar, a simple majority, for changing the Constitution. They also say banning same-sex marriage is an issue that will play well with the state’s large Hispanic population, which tends to hold somewhat more conservative social views.
The state’s electorate seems divided. A 2007 poll by the Public Policy Institute of California found 49 percent of residents opposed to same-sex marriage, and 45 percent in favor.
Gavin Newsom, the mayor of San Francisco, who added to the national debate about same-sex marriage in 2004 when he ordered the county clerk to issue marriage licenses to gay couples, said it would be important to the fall campaign to perform marriages as soon as possible.
Mr. Staver, of Liberty Counsel, said he would ask for a stay of the court’s ruling until voters could decide, but Mr. Newsom is not interested in waiting.
“As we move forward and literally tens of thousands of couples are married, the question to the voters changes,” Mr. Newsom said. “It’s no longer denying something to people that they never had. It’s taking something away that they’ve already enjoyed. And that’s a much more difficult thing to do.”
Some couples are planning to combine their weddings with efforts to make sure their legal unions are not short-lived. Cary Davidson, a lawyer who lives in Los Angeles and is a member of the Equality California board, said he and his partner, Andrew Ogilvie, planned to marry before the November election.
But he said they would ask guests to contribute to the campaign to defeat the ballot measure instead of buying gifts.
“The only thing that matters to us at the moment is to make sure that the rights that we just gained are maintained,” said Mr. Davidson, 53, who has been with Mr. Ogilvie for 18 years. “And that’s the best way to do it.”