Last week’s decision by the California Supreme Court makes that state the second to legalize same-sex marriage. Opponents vow to mount a ballot question in November that would void the ruling. But should they fail, the Golden State will join Massachusetts in extending marital privileges to homosexual couples.

While acceptance of homosexuality has grown steadily in recent years, Americans have widely resisted gay marriage. More than half the states have constitutional amendments prohibiting it, or defining marriage as being between a man and a woman. This fall, depending on voters’ preferences, Florida could join them. (Rhode Island is a blank slate, neither prohibiting nor allowing same-sex marriage.)

Perhaps not surprisingly then, California’s high court was closely divided. By 4 to 3, it found that marriage was a fundamental constitutional right, and that denying it on the basis of sexual preference could not be justified by “tradition alone.” Drawing an analogy with interracial marriage, which California approved years ahead of the rest of the country, it also noted that a ban offends notions of equality.

Foes are tarring this decision as an act of meddling by “activist” judges. In any event, six of the seven justices hearing the case were Republican appointees. And GOP Gov. Arnold Schwarzenegger, who twice vetoed bills to allow gay marriage, said he would accept the ruling.

Despite resistance among social conservatives, it appears that America is headed, eventually, for acceptance of same-sex marriage. The California ruling, if it sticks, will affect a far more significant population than now falls under Massachusetts law. (An estimated 92,000 same-sex couples reside in California.) Gays who wed there will help accustom others to this quiet revolution — chiefly by demonstrating that they can be as drained, dulled and divided over housekeeping duties and expenses as anyone else.

Perhaps just as importantly, polls reveal younger Americans as far more accepting than their elders of homosexual relationships. This suggests that, in another generation, much of the fuss will simply wither.

No one would say that marriage is easy. But it affords stability, support and the deep satisfactions that come with commitment. It is also a fine foundation for nurturing families. That people have been denied the privileges of marriage because of their sexual orientation is both sad and unjust. Certainly we have not heard the last of this debate. But the California ruling is a key step in a historic journey.