New York Assemblyman Daniel O’Donnell (D-Manhattan), the gay brother of TV personality Rosie O’Donnell, introduced a bill this week to legalize same-sex marriage in the state.

O’Donnell’s action appears to have broken ranks with New York’s Democratic governor, Andrew Cuomo, who promised to introduce marriage equality legislation but has hesitated in doing so just weeks before the state legislature is scheduled to adjourn for the year.

Cuomo, a strong backer of same-sex marriage, reportedly has persuaded a coalition of LGBT advocacy groups campaigning for a marriage bill to support his plan to hold off on introducing the bill until enough votes could be lined up to pass it in the Republican-controlled state Senate.

“It is with great pride that I am introducing the Marriage Equality Act,” O’Donnell said in a statement. “Since the Assembly last passed the bill in 2009, there has been an overwhelming groundswell of support for marriage equality across our state.”

The Democratic-controlled Assembly has passed a same-sex marriage bill three times since 2007, and this is the fourth time O’Donnell has emerged as the lead sponsor of the bill. But the bill lost in the Senate in 2009 by an eight-vote margin at a time when Democrats controlled the body. It was the first time the Senate had taken a vote on the measure.

Josh Vlasto, a spokesperson for Cuomo, told the New York Times on Tuesday that the governor remains committed to seeing the bill pass before the legislature adjourns at the end of June.

“The question has never been the Assembly,” Vlasto told the Times. “The question has always been whether there are the votes in the Senate, and that remains the question.”

Vlasto’s comments came at a time when many political observers in the state were hopeful that between four and six Republican senators would join as many as 28 Senate Democrats to secure the bill’s passage. Most observers expect the Assembly to once again approve the bill.

Republicans have a 32-30 majority in the 62-member Senate.

Supporters, led by a coalition of LGBT groups, including the Empire State Pride Agenda (ESPA) and the Human Rights Campaign, have pointed to a recent public opinion poll showing that 58 percent of New Yorkers support the right of gay and lesbian couples to marry.

Advocates for the bill also note that Cuomo, who has a high public approval rating, is aggressively lobbying both Democratic and Republican lawmakers to vote for a marriage equality bill that he says he wants to personally introduce.

“We think the environment is strong,” said ESPA Executive Director Ross Levi. “To have such a popular governor so forcefully behind it, to have the public so solidly on our side at 58 percent, to have the LGBT community and so many strong allies working closely and coordinated together creates a good environment to work on this and achieve victory,” he said.

In a development that was long expected, the anti-gay National Organization for Marriage announced this week it is launching a $500,000 TV ad campaign to defeat the marriage bill. The group has also vowed to spend $1 million to defeat any Republican lawmaker who votes for the bill and to support the re-election of any Democratic legislator who votes no on the bill.

“It’s become quite clear in recent days in New York that Gov. Cuomo and same-sex marriage advocates are targeting a select number of Democrat state senators, as well as some Republicans, in their desperate attempt to coerce legislators to support their agenda,” said NOM President Brian Brown.

“We want to be sure those courageous Democrats and Republicans who cast their vote of conscience in favor of traditional marriage will have a strong supporter if the radical gay activists come after them in their next election,” Brown said.

Similar to its practice in other states, NOM’s TV ad opposing the bill, which aired on TV stations this week, claims that legalizing same-sex marriage would result in elementary schools teaching children about gay marriage and how it benefits society.

The Human Rights Campaign has responded by launching its own campaign to challenge the NOM ads, saying the group is falsely linking marriage equality to school curricula.

“We’re fighting for loving committed gay and lesbian couples going down to the courthouse to get married, which has absolutely nothing to do with what is taught in schools,” said HRC President Joe Solmonese. “The ad is a piece of fiction,” he said. “School districts determine what is taught in schools.”

NOM’s Brown argues that the “message” it conveys in its TV ads has resonated in all states in which same-sex marriage bills have come before voters in a referendum. He said NOM’s campaign against same-sex marriage also has been successful in states where gay marriage surfaced in legislatures.

“In Maryland and Rhode Island we just won great victories for marriage,” he said. “Our opponents tried to claim that same-sex marriage was inevitable in both states. They were wrong. Once our message got out and legislators heard from their constituents, same-sex marriage was stopped dead,” he said. “We expect the same to happen in New York.”

Levi said the New York coalition working to pass marriage equality legislation has learned from mistakes made by advocates in other states, including Maryland.

The coalition, called New Yorkers United for Marriage, includes ESPA, HRC, Freedom to Marry, and Log Cabin Republicans. It has launched its own TV ads in support of the marriage equality bill in all parts of the state, according to Levi.

He said more than 1,200 LGBT advocates and their allies descended on the state capital in Albany on Monday in an ESPA-led rally in support of the marriage bill. Participants, among other things, visited the offices of senators as Assembly members to urge them to vote for the measure.

HRC, meanwhile, has been releasing a series of videos in the state featuring testimonials in support of the bill by celebrities, including actors Julianne Moore and Sam Waterston and President George W. Bush’s daughter, Barbara Bush. Former President Bill Clinton issued a written statement supporting the bill last week.

New York Rangers star hockey player Sean Avery surprised the sports world by agreeing to appear in one of HRC’s videos expressing strong support for the marriage bill, becoming one of the nation’s first major sports figures to embrace a gay rights issue.

Levi said the timing of introducing a same-sex marriage bill in the New York Legislature isn’t as important as securing the support from the speaker of the Assembly and the majority leader of the Senate, who have full control over which bills come up for a vote. The Assembly speaker has long been supportive of the bill.

Senate Majority Leader Dean Skellos (R-Long Island) has said he would allow the bill to reach the Senate floor for a vote even though Skellos announced he would vote against it.

According to Levi, the November 2010 election in New York resulted in at least two more senators who have publicly committed to voting for the marriage measure. But Levi was cautious about predicting the outcome of a Senate vote, saying he was optimistic that the bill would pass.

“We’re not taking anything for granted and we’re working carefully in both chambers, particularly talking to new legislators about why this issue is important,” he said. “We’re doing that in both the Assembly and the Senate.”