By Edith Honan

NEW YORK (Reuters) - Gay rights activists are renewing their fight to legalize same-sex marriage in New York, hoping a mix of moneyed supporters and celebrity star power will tilt the scales in their favor.

A group called Fight Back New York, created with money from software entrepreneur and openly gay philanthropist Tim Gill, is pledging to spend hundreds of thousands of dollars to get pro-gay marriage candidates elected to the state Senate in November's elections.

Advocates aim to bring the issue of same-sex marriage to the Senate floor as early as next year. The legislature voted three months ago to reject a similar bill.

"There is definitely a theme of punishment in our work," said spokesman Alex Navarro-McKay. The group would target some of the eight Democrats who helped defeat the bill, he said. All 30 Republicans and eight Democrats voted no, defeating the bill 38 to 24.

Five U.S. states have legalized gay marriage -- Iowa, Connecticut, Massachusetts, New Hampshire and Vermont -- and the District of Columbia began allowing same-sex marriages earlier this month.

But 40 other states have specific laws banning it. Voters in Maine repealed a gay marriage law recently, and the New Jersey legislature rejected a gay marriage bill.

A federal court in California is now hearing a legal challenge to the state's ban on gay marriage, known as Proposition 8, that was approved by voters in 2008.

This week, Fight Back New York claimed victory when a candidate who has a record of supporting gay marriage won a special election to succeed Hiram Monserrate, who voted against the marriage bill. Monserrate was expelled from the New York Senate after being convicted of assaulting his girlfriend.

"One down, seven to go," the group said in a statement.

Maggie Gallagher, president of the National Organization for Marriage which opposes same-sex marriage, said gay rights advocates face an uphill battle.

"They no longer are persuading people that gay marriage is a good idea," she said. "I don't think it's very credible to claim that this victory is some sort of bellwether for the popularity of gay marriage in elections in New York.

RECRUITMENT TOOL

Advocates say the defeat of measures in New York and elsewhere can be a valuable recruitment tool.

"As awful as Prop 8 was, I think people will say it was the moment that lit the fire," said Rory O'Malley, an actor and a founder of Broadway Impact, an organization of theater professionals who support same-sex marriage.

"Sex and the City" actress Cynthia Nixon has lent her celebrity power to Fight Back New York, while so many plays on and off Broadway are evoking gay issues that The New York Times dubbed it "the unofficial spring festival of gay theater."

One play, "The Temperamentals," about the Mattachine Society, which fought for gay rights in the 1950s, is followed on Monday nights by discussion of gay rights. The plays "The Pride" and "Next Fall" also deal with gay rights issues.

"These plays were obviously written and conceived as our society has grappled with, 'How do you deal with these issues?'" said state Assemblyman Daniel O'Donnell who sponsored the gay marriage bill last year. "Now they're requiring people to talk about ... 'Why does our state deprive certain people of a license?'"

The brother of television personality Rosie O'Donnell, he added that celebrity power only goes so far. "I've lived in the shadow of celebrity ... and I totally and fully understand its power and how it can be helpful," he said.

Dennis Proust, spokesman for the New York State Catholic Conference, which opposes same-sex marriage, said there was no evidence that the political winds will change in New York.

"I think it would be a huge mistake to bring it to the floor a second time and have it be soundly defeated," said Proust. "Not only did they not win, they got creamed."