But that triumph might be short-lived, as opponents attacked the ruling immediately after it was released yesterday morning and readied for a potential November vote on a constitutional amendment that could make the court's historic decision moot.

In a 4-3 ruling, the state's highest court said two state laws, one of which was approved by voters, are unconstitutional discrimination because they limit marriage to opposite-sex couples.

California becomes only the second state in the country to legalize same-sex marriage – Massachusetts was first.

Yet because the state Supreme Court is considered one of the most influential state high courts in the nation – its opinions are cited more frequently than any other state court – proponents said they hoped the court's stature would affect laws in other states.

But all that was secondary for same-sex marriage supporters, who reacted with elation and some surprise.

“This decision is a powerful affirmation of love, family and commitment,” said Shannon Minter, the legal director for the National Center for Lesbian Rights who argued the case in front of the court in March.

“I'm happy, I'm astounded, I'm thrilled,” said Janet Wallace, a San Francisco woman who, along with her partner of 17 years, was one of the plaintiffs in the case.

Opponents deplored the ruling. “It's just breathtakingly broad judicial activism the court engaged in today,” said Jordan Lorence of the Alliance Defense Fund.

Decided to overturn same-sex marriage ban Chief Justice Ronald M. George 68 Year sworn: July 1991 Appointed by: Gov. Pete Wilson Justice Joyce L. Kennard 67 Year sworn: April 1989 Appointed by: Gov. George Deukmejian Justice Carlos R. Moreno 59 Year sworn: October 2001 Appointed by Gov. Gray Davis Justice Kathryn M. Werdegar 72 Year sworn: May 1994 Appointed by Gov. Pete Wilson Decided to uphold same-sex marriage ban Justice Marvin R. Baxter 68 Year sworn: January 1991 Appointed by Gov. George Deukmejian Justice Ming W. Chin 65 Year sworn: March 1996 Appointed by Gov. Pete Wilson Justice Carol A. Corrigan 59 Year sworn: January 2006 Appointed by Gov. Arnold Schwarzenegger

The group defended Proposition 22, the measure voters approved in 2000 that explicitly defined marriage as being between a man and a woman. It was one of the laws struck down yesterday.

Lorence said the group is considering asking the court to issue a stay on the decision, which is scheduled to take effect in 30 days, until after the November election.

Opponents hope to qualify an initiative for the November ballot that would amend the state constitution and ban same-sex marriage, thus trumping the Supreme Court decision.

Some religious groups also criticized the ruling. The California Catholic Conference of Bishops said the decision “opens the door for policymakers to deconstruct traditional marriage and create another institution under the guise of equal protection.”

The court's opinion, written by Chief Justice Ronald George in careful and often dense legal prose, rested on two main points. George said state laws banning same-sex marriage violated the right to marry embodied in the state constitution.

While the constitution does not explicitly contain this right, George said previous court decisions have established it. Among those was the court's historic 1948 decision striking down a law banning interracial marriage – California was the first state to do so.

The right to marry “guarantees same-sex couples the same substantive constitutional rights as opposite-sex couples to chose one's life partner and enter with that person into a committed, officially recognized and protected family relationship that enjoys all of the constitutionally based incidents of marriage.”

The majority also said laws banning same-sex marriage violated the equal protection rights of citizens because they discriminated on the basis of sexual orientation.

Supporters of the ban, including the Attorney General's Office that defended it before the court, said the justices should abide by the historic understanding of marriage as being between a man and a woman.

But George swept aside that reasoning, writing that “tradition alone” could not be used to justify denial of a fundamental constitutional right.

He also wrote that same-sex couples who marry will have the same “duties and obligations” to their children, spouses and others as heterosexual couples have. Allowing same-sex marriage, George said, will not harm heterosexual couples – but blocking gays and lesbians from marriage does hurt them.

Justice Marvin Baxter led the dissent. He said the majority had created “a constitutional right from whole cloth.”

Moreover, he wrote, “a bare majority of this court, 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.”

Baxter said the legislature or voters should change the law, if they wished. He was joined by Justice Ming Chin. The newest justice, Carol Corrigan, also dissented in a separate opinion.

Joining George in the majority were justices Kathryn Werdegar, Joyce Kennard and Carlos Moreno.

The state has a domestic partnership law that confers many of the rights of married couples to same-sex couples. But the court ruled such a parallel system makes gay and lesbian couples “second-class citizens” and can't substitute for full-fledged marriage.

The case combined lawsuits filed in 2004 by same-sex couples in San Francisco and Los Angeles and one from the city and county of San Francisco that challenged the marriage laws.

The issue was initially forced on the courts when on Valentine's Day 2004, San Francisco Mayor Gavin Newsom said the city would offer marriage licenses to same-sex couples. Some 4,000 couples got licenses, but those were declared void by the high court later that year in a separate case that dealt with issues other than the validity of same-sex marriage.

Newsom said yesterday the Supreme Court “took a bold and important step forward to end discrimination in California.”

After Newsom ignited the issue, it methodically worked its way through the legal system. In 2005, a San Francisco trial court judge ruled in favor of the plaintiffs.

But in 2006 an appeals court reversed that decision. That court said the law did not discriminate based on gender and the state had a right to preserve the definition of marriage.

That was the ruling the Supreme Court overturned.

When the court's decision becomes final in 30 days, a flood of eager couples could descend on county clerk's offices across the state.

Some may come from other states because California does not have a residency requirement for marriage. However, other states may not recognize marriages in California, because each state has its own marriage statutes. The federal government also does not recognize same-sex marriages.

Greg Smith, San Diego County's assessor, recorder and clerk, said county lawyers have advised him not to issue marriage licenses to same-sex couples until the state creates forms for the process.

Smith said he's in a “holding pattern” until he gets direction from the state. His office received about two dozen calls about same-sex marriage after the Supreme Court's decision yesterday. At least one gay couple went to the office and was turned away.

Staff writer Craig Gustafson contributed to this report.

Greg Moran: (619) 542-4586; greg.moran@uniontrib.com