ALBANY — For gay rights advocates, yesterday’s vote in the Assembly to legalize same-sex marriage was a watershed moment to be celebrated. For many lawmakers in the chamber, it was a day of hard political calculations, painful choices, and apprehension.

The Democrat-led Assembly last night voted to 85 to 61 to allow same-sex couples to wed in New York, the first time that a legislative body in the state has approved gay marriage. The vote pushed New York closer to becoming the second state in the nation to legalize gay marriage, after Massachusetts, and the first to do so through a legislative process.

About 80% of Democrats in the body voted in favor of the bill; only four out of 42 Republicans did so.

All 12 Manhattan Assembly members backed the legislation, including Speaker Silver, while support was weaker in Brooklyn (11 Democrats for; seven, including Diane Gordon, Dov Hikind, and Steven Cymbrowitz against, two absent); Queens (15 Democrats for, three, including Margaret Markey, against); the Bronx (seven Democrats for; three against, one absent); and Staten Island (three Democrats for, one Republican against).

Gay marriage has enjoyed support in Manhattan Assembly districts for years; passage of the bill hinged on votes from other members, some of whom conceded they were taking a political risk. Polls show that slightly more New Yorkers oppose gay marriage than favor it, with opposition strongest among older residents, who are typically more likely to vote.

Lawmakers who were on the fence said they made up their minds after having conversations with constituents, religious leaders, and family members. They said their choice was result of a push-and-pull between political considerations and personal feelings.

Those with statewide ambitions had to weigh the sentiments of their districts against statewide trends that show gay marriage gaining acceptance. Younger members who rely on religious institutions for political support were more likely to oppose gay marriage.

Assemblyman Darryl Towns, an African-American who represents Brooklyn’s Bushwick and East New York, where a high percentage of residents are Catholic and Baptist, voted for the bill. “I’m not sure that civil rights leaders had drawn lines to add a caveat about what they would and wouldn’t fight for.”

Mr. Towns, whose grandfathers were both ministers, said he decided to vote for the bill after having conversations with his uncle, the retiring senior minister of Riverside Church, James Forbes.

Assemblyman Carl Heastie, a Baptist who represents a Bronx district with a large Caribbean population and many Baptist, Episcopal, and Methodist residents, voted against gay marriage. He said the leaders of several churches in his district, including Trinity Baptist Church, and Bronx Bethany Church, were “united” against gay marriage.

“I’m very sympathetic to human rights issues, but this is a tough vote for me,” he said. “Before you worry about your political future, you have to worry about your political present.”

Assemblywoman Ann Margaret Carrozza, a Democrat who represents Bayside, Queens, where there are many conservative Catholic voters, voted for the bill and said she was not concerned about the political repercussions. “In three to five years, this is going to be a non-issue,” she said.

For three hours last night, gay marriage was debated before a packed chamber, with just about every Assembly member sitting in rapt attention and dozens of state senators looking on. Just as the debate began, storm clouds blotted out the sun.

Mr. Hikind, an Orthodox Jew who represents Borough Park in Brooklyn, warned that lawmakers by supporting gay marriage were paving the path toward sanctioning incest. He said he would support gay marriage if God gave him a signal. Moments later, there was a loud crack of thunder, provoking laughter.

With Governor Spitzer, a Democrat, strongly in favor of legalizing gay marriage, the battle now shifts to the Senate, which has leaned leftward on a number of social issues in recent years but has shown little indication that it intends to follow the Assembly’s lead.

Even if Democrats take control of the Senate, which has a slim Republican majority, gay rights advocates say it could take years before a gay marriage bill arrives on the governor’s desk.