SAN FRANCISCO (AP) — California’s Supreme Court declared that gay couples in the nation’s biggest state can marry — a monumental but perhaps short-lived victory for the gay rights movement Thursday that was greeted with tears, hugs, kisses and at least one instant proposal of matrimony.

Same-sex couples could tie the knot in as little as a month. But the window could close soon after — religious and social conservatives are pressing to put a constitutional amendment on the ballot in November that would undo the Supreme Court ruling and ban gay marriage.

‘‘Essentially, this boils down to love. We love each other. We now have equal rights under the law,’’ declared a jubilant Robin Tyler, a plaintiff in the case along with her partner. She added: ‘‘We’re going to get married. No Tupperware, please.’’

A crowd of people raised their fists in triumph inside City Hall, and people wrapped themselves in the rainbow-colored gay-pride flag outside the courthouse.