The California Supreme Court, striking down two state laws that had limited marriages to unions between a man and a woman, ruled Thursday that same-sex couples have a state constitutional right to marry.

The 4-3 decision, drawing on a ruling 60 years ago that struck down a state ban on interracial marriage, would make California the second state, after Massachusetts, to allow same-sex marriages.

The decision, which becomes effective in 30 days unless the court grants a stay, was greeted with celebrations at San Francisco City Hall, where thousands of same-sex marriages were thrown out by the courts four years ago.

The court decision was denounced by religious and conservative groups that promised to support an initiative proposed for the November ballot that would amend the state constitution to ban same-sex marriages and overturn the decision.

Same-sex marriage has been a highly contentious issue in presidential and congressional elections, but it was not immediately clear what role the ruling would have this year. The Democratic and Republican candidates for president have all said they believe marriage should be between a man and a woman, but Republicans could use a surge in same-sex marriages in the most populous state to invigorate conservative voters.

Given the historic, cultural, symbolic and constitutional significance of marriage, Chief Justice Ronald M. George wrote for the majority, the state cannot limit its availability to opposite-sex couples.

"In view of the substance and significance of the fundamental constitutional right to form a family relationship," George wrote, "the California Constitution properly must be interpreted to guarantee this basic civil right to all Californians, whether gay or heterosexual, and to same-sex couples as well as to opposite-sex couples."

Supporters of same-sex marriage called the ruling a milestone.

"This decision will give Americans the lived experience that ending exclusion from marriage helps families and harms no one," said Evan Wolfson, executive director of Freedom to Marry.

Opponents said they expected the proposed ballot initiative, which has been submitted to election officials with more than 1 million signatures, to pass in November.

"The court was wrong from top to bottom on this one," said Maggie Gallagher, president of the National Organization for Marriage. "The court brushed aside the entire history and meaning of marriage in our tradition."

About 110,000 same-sex couples live in California, according to census data. The state has a strong domestic partnership law that gives couples who register nearly all of the benefits and burdens of heterosexual marriage.

A majority of the justices said that was not enough.

The court left open the possibility that the Legislature could use a term other than "marriage" to denote state-sanctioned unions, so long as that term was used across the board for opposite-sex and same-sex couples.

The ban on same-sex marriage was based on a law enacted in 1977 and a statewide initiative approved by the voters in 2000, both defining marriage as limited to unions between a man and a woman. The question before the court was whether those laws violated provisions of the California Constitution protecting equality and fundamental rights.

Request for a stay

Mathew D. Staver, a lawyer with Liberty Counsel, a public interest firm that defends traditional marriage, said it would ask the court to stay its decision until the November election, meaning that the decision could be overturned before becoming effective.

"It would only be logical" to grant a stay, Staver said, given the confusion that would arise if same-sex marriages were available for a few months.

Gov. Arnold Schwarzenegger, a Republican, said in a statement that he respected the ruling and did not support a constitutional amendment to overturn it.

In a dissent, Justice Marvin R. Baxter said the majority should have deferred to the Legislature on whether to allow same-sex marriage, particularly given the increased legal protections for same-sex couples enacted in recent years.

"But a bare majority of this court," Baxter wrote, "not satisfied with the pace of democratic change, now abruptly forestalls that process and substitutes, by judicial fiat, its own social policy views for those expressed by the People themselves."

Also dissenting, Justice Carol A. Corrigan wrote that her personal sympathies were with the plaintiffs challenging the bans on same-sex marriage. But Corrigan said the courts should allow the political process to address the question.

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