Local veterans of Massachusetts' long battle over gay marriage responded swiftly Thursday to the California Supreme Court ruling that same-sex couples have a constitutional right to marry.

The 4-3 decision by California's top court would make it the first state in the nation to join Massachusetts in allowing gays and lesbians to wed.

Despite California's comprehensive domestic partnership law, the court's single-vote majority said limiting marriage to opposite-sex couples is discriminatory.

In fact, the Republican-dominated court's judgment was even more sweeping than the 2004 ruling in Massachusetts, because the justices there are the first to rule that individuals should be protected from bias based on their sexual orientation in the same way that they are protected from racial or gender bias.

The landmark decision won immediate praise from U.S. Rep. Barney Frank, D-Newton, whose district includes Foxboro, Norfolk, Norton and Mansfield and who is openly gay and has spent years advocating for gay rights. "I can assure the people of (California) that the result of this decision will be to improve the quality of life of tens of thousands of Californians who will now be able legally to express their love for each other, while having no negative effect whatsoever on the overwhelming majority of Californians who will choose not to marry someone of the same sex," Frank said in a statement.

Joe Solmonese, an Attleboro native who heads up the national gay rights group Human Rights Campaign, called Thursday "a historic day."

"The California Supreme Court has made clear that same-sex couples in committed relationships and their families deserve the same level of respect afforded to opposite-sex couples," Solmonese said. "The court did its job by ensuring that the state constitution provides the same rights and protections for everyone."

The court's ruling ordered that local authorities in California begin recognizing same-sex marriages in 30 days. But opponents of the decision said they would ask the court to postpone that deadline until after the November election, when they hope to pass a constitutional amendment that would undo the ruling and ban gay marriage.

That's the right course of action, according to former Massachusetts state Rep. Philip Travis, D-Rehoboth, who led the fight on Beacon Hill against legalizing gay marriage here until his retirement in 2006.

"They're going to have to abide by the law, the same as in Massachusetts," he said in an interview late Thursday. "They will go to a referendum and try to change it, like we did. I don't know how many years it will take. I don't even want to try and predict the outcome."

In Massachusetts, the outcome was a victory for gay marriage supporters. The Legislature voted last summer not to place on the November ballot a proposed state constitutional amendment that would have banned gay marriage.

Travis, who has been in touch with same-sex marriage opponents in California and elsewhere, also said critics of the ruling should not turn the argument into a personal one.

"I would implore the people of California to be civil about it," he said. "Don't become uncivil and call other people names. That isn't what it's supposed to be all about."

Travis added, "It is the law of California now. Don't get upset and take issue with them getting married. It's their wedding and wish them well. But if you take a different stance, as I do, go and try to win the war." TED NESI can be reached at tnesi@thesunchronicle.com or 508-236-0333.