A decision by gay couples to wed represents "a personal expression of emotional devotion, support and interdependence and a public commitment," state Supreme Court Judge Lucy Billings wrote in a decision issued Tuesday. "With that validity, they expect equal treatment with other married couples."

Thousands of gay New Yorkers over the next few years are expected to make use of Massachusetts' recent decision to let out-of-state gay couples marry there. The Christian legal organization that brought the New York case said it would appeal, while gay-rights and civil-liberties groups hailed the ruling as strengthening legal support for same-sex couples.

In a statement, Gov. David Paterson called it "a wise and fair determination."

Same-sex couples cannot marry in New York, and the state's highest court has said only the Legislature has the authority to change that. But Paterson's counsel told state agencies in May that a recent state appellate court ruling required them to recognize gay marriages legally performed elsewhere or risk discrimination claims.

The directive prompted a lawsuit from the Alliance Defense Fund, an Arizona-based group that has repeatedly challenged attempts to extend spousal rights to gay couples in New York. Several Republican state senators had signed onto the latest suit.

The alliance is involved in cases around the country that concern gay marriage, abortion, school prayer and other social issues. It already had several ongoing cases over attempts to extend spousal rights to gay couples in New York.