ALBANY — After much debate and wrangling, the Democrat-led Assembly as early as today is set to approve legislation legalizing same-sex marriage, handing gay rights advocates in the Empire State a major symbolic victory.

The speaker of the Assembly, Sheldon Silver, who represents a district in Lower Manhattan, agreed to put the bill up for a floor vote this week after his staff concluded that it had more the minimum 76 votes to pass the chamber. Still, some lawmakers said they expected some lawmakers to change their mind.

It would be the first time that a legislative chamber in New York has approved gay marriage and the second time that a legislative body in America has passed such a law.

With Governor Spitzer supporting the legislation, the Republican-led Senate remains the one source of powerful opposition against gay marriage. Advocates say they are preparing for a long lobbying battle, and it may take years before New York joins Massachusetts in allowing same-sex couples to wed.

Gay rights advocates are counting on the Assembly’s action to set in motion a debate in the Senate. “What the Senate does is wait for the Assembly to move, and sometimes they wait for years, but the catalyst is the passage in the Assembly,” the bill’s sponsor in the Assembly, Daniel O’Donnell, who is openly gay, said.

“The Assembly has always been the vanguard of civil rights legislation,” the executive director of the Empire State Pride Agenda, Alan Van Capelle, said. Mr. Capelle, who made dozens of trips to Albany to buttonhole Assembly members who were opposed or undecided, said his organization would focus all of its attention on the Senate next year.

Mr. Silver has not taken a position but is expected to vote for the measure. While Assembly Democrats have been traditionally supportive of gay rights legislation, they have been reluctant to wade into the gay marriage debate and risk retribution from voters.