SAN FRANCISCO — The California Supreme Court struck down the state's ban on same-sex marriage yesterday in a broadly worded decision that would invalidate virtually any law that discriminates on the basis of sexual orientation.

The 4-3 ruling declared that the state Constitution protects a fundamental "right to marry" that extends equally to same-sex couples. It tossed a highly emotional issue into the election year while opening the way for tens of thousands of gay people to wed in California, starting as early as mid-June.

The majority opinion, by Chief Justice Ronald M. George, declared that any law which discriminates on the basis of sexual orientation will from this point on be constitutionally suspect in California in the same way as laws which discriminate by race or gender, making the state's Supreme Court the first in the nation to adopt such a stringent standard.

The decision was a surprise from a moderately conservative, Republican-dominated court which legal scholars have long dubbed "cautious," and experts said it was likely to influence other courts around the country.

But the scope of the court's decision could be thrown into question by an initiative already heading toward the November ballot. The initiative would amend the state Constitution to prohibit same-sex unions.

CAMPAIGNING UNDERWAY

The campaign over that measure began within minutes of the decision. The state's Catholic bishops and other opponents of gay marriage denounced the ruling. But Gov. Arnold Schwarzenegger issued a statement saying he respects the decision and "will not support an amendment to the constitution that would overturn" it.

The ruling was greeted with cheering and whooping when it was released at the Supreme Court's headquarters yesterday. People lined up outside to buy a copy of the decision for $10 each.

Gay groups planned celebrations up and down the state.

Conservative and religious-affiliated groups denounced the decision and pledged to bring enough voters to the polls in November to overturn it. Mathew Staver, founder of Liberty Counsel, called the decision "outrageous" and "nonsense."

The decision came after supreme courts in New York, Washington and New Jersey refused to extend marriage rights to gay couples. Only Massachusetts' top court has ruled in favor of permitting gays to wed.

The court's ruling repeatedly invoked the words "respect and dignity" and framed the marriage question as one that deeply affected not just couples, but also their children. California has more than 100,000 households headed by gay couples, about a quarter with children, according to 2000 Census data.

"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. "An individual's sexual orientation — like a person's race or gender — does not constitute a legitimate basis upon which to deny or withhold legal rights," he continued.

OVERRULES PROP 22

Many gay Californians said that even the state's broadly worded domestic partnership law provided only a second-class substitute for marriage. The court agreed.

Giving a different name, such as domestic partnership, to the "official family relationship" of same-sex couples imposes "appreciable harm" both on the couples and their children, the court said.

The distinction might cast "doubt on whether the official family relationship of same-sex couples enjoys dignity equal to that of opposite-sex couples," George wrote, joined by Justices Joyce Kennard, Kathryn Mickle Werdegar and Carlos Moreno. All but Moreno were appointed by Republican governors. George was appointed by Gov. Pete Wilson in 1991.

The ruling cited a 60-year-old precedent that struck down a ban on interracial marriage in California. The three dissenting justices argued that it was up to the electorate or the Legislature to decide whether gays should be permitted to marry.

In 2000, 61 percent of California voters approved a ballot measure, Proposition 22, that said "only marriage between a man and a woman is valid and recognized in California."

Since then, the legislature has passed one of the strongest domestic partnership laws in the country, giving registered same-sex couples most of the rights of married people.

"In my view, California should allow our gay and lesbian neighbors to call their unions marriage," Justice Carol Corrigan wrote in the first sentence of her dissent.

"But I, and this court, must acknowledge that a majority of Californians hold a different view, and have explicitly said so by their vote. This court can overrule a vote of the people only if the Constitution compels us to do so. Here, the Constitution does not."

The decision takes effect in 30 days. Gay couples would then be permitted to marry in California, even if they do not live in the state, gay rights lawyers said. Under federal law, however, other states would not have to recognize those marriages as valid. And same-sex couples would remain ineligible for certain federal benefits, including Social Security benefits for spouses and joint filing for income taxes.

Times staff writers in Sacramento, Los Angeles and San Francisco contributed to this report.