ALBANY - New York took a dramatic turn toward legalizing gay marriage as key changes in positions Monday brought supporters to within two votes of what is required for State Senate passage.

A Rochester-area Republican Monday became the first GOP senator to announce his support for making same-sex marriage legal and three Democrats reversed their previous opposition. That meant that at least 30 of New York's 62 state senators now openly back the idea. Thirty-two votes are needed for Senate passage.

Gov. Andrew M. Cuomo, who has made the issue one of his key priorities of the legislative session, was to introduce a gay-marriage bill late Monday, setting the stage for a vote later this week. Advocates saw that as a major milestone because the governor has warned that he would not push for a vote if he thought it would fail.

The Democrat-led Assembly has passed the measure in previous years and is expected to do so again.

Supporters are cautiously expecting that at least two more Senate Republicans will eventually support the measure, now that Sen. James Alesi (R-Perinton) has opened the gates.

Alesi, who voted against a gay marriage bill in 2009 when it was defeated in the Senate, announced his reversal after a late afternoon meeting with the governor. Alesi called his no vote two years ago "anguishing" and said he did it for political reasons -- because Republicans had decided to vote against it in a bloc.

"I've apologized for letting people down, but I was supporting a conference vote that I believed at the time politically was necessary when we [Republicans] were in the [Senate] minority," Alesi said, essentially saying that the GOP didn't want to give the Democrats who then controlled the chamber a victory.

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He called his new stance liberating. "I believe that if you live in America and you expect equality and freedom for yourself, then you have to extend it to other people," Alesi said.

Alesi indicated he was not overly concerned with losing the support of the Conservative Party -- whose leader has vowed not to endorse any candidate who backs gay marriage. Many observers thought that threat might intimidate moderate Republicans, who have at times depended on the minor party's backing in close races.

Earlier, Democrats announced that three of their own senators had changed their position, meaning 29 of their 30 members now support gay marriage. The lone holdout is Sen. Ruben Diaz (D-Bronx), a Pentecostal minister.

None of Long Island's nine senators -- all Republicans -- have indicated whether they would favor changing the law.

Senate Majority Leader Dean Skelos (R-Rockville Centre) said Republicans will discuss the issue in a closed-door conference either Tuesday or Wednesday to determine whether to bring a bill to the floor for a vote before the end of the legislative session, slated for June 20. Cuomo hosted Senate Republicans at a dinner at the Executive Mansion Monday night to discuss the issue, along with other legislation.

"I've always indicated it going be a conscience vote," as opposed to political, Skelos said earlier in the day. "I've always said if they [are] for it, they should vote for it. I'm not going to make it a party vote."

Though still hedging about the eventual outcome, activists clearly saw the Alesi turnaround as crucial. "We continue to think the environment is strong," said Ross Levi, head of the Empire State Pride Agenda.