LOS ANGELES — On a warm Friday afternoon three years ago, Rob Reiner, the director, arrived for lunch at the Beverly Hills estate of David Geffen, the entertainment mogul. Mr. Reiner and his political adviser, Chad H. Griffin, had spent six months drafting an ambitious legal campaign aimed at persuading the United States Supreme Court to establish a constitutional right of same-sex marriage.
Mr. Reiner, joined by Mr. Griffin and Mr. Reiner’s wife, Michele, told Mr. Geffen they would need $3 million to challenge Proposition 8, a California voter initiative approved the previous November banning same-sex marriage. He informed Mr. Geffen that they had recruited two renowned lawyers, David Boies, a Democrat, and Theodore B. Olson, a Republican, to argue the case.
“Our feeling is not to go state by state,” Mr. Reiner said. “Our strategy is to make this wind up in the United States Supreme Court and have this a settled issue for all time.”
Mr. Geffen asked few questions as they sat in the dining room off his screening room, with a sweeping view down his sculptured estate. He agreed before the dessert arrived to raise the money. “I said I’d give them half the money and raise the other half,” Mr. Geffen recalled. Mr. Geffen wrote a check for $1.5 million and asked Steve Bing, a friend and producer, to make up the rest.
That lunch was a milestone in the dramatic evolution of a behind-the-scenes fund-raising network whose goal is to legalize same-sex marriage from coast to coast. This emerging group of donors is not quite like any other fund-raising network that has supported gay-related issues over the past 40 years. They come from Hollywood, yes, but also from Wall Street and Washington and the corporate world; there are Republicans as well as Democrats; and perhaps most strikingly, longtime gay organizers said, there has been an influx of contributions from straight donors unlike anything they have seen before.
Mr. Griffin, who this month was named president of the Human Rights Campaign, a national gay advocacy group, recalled being at a September 2010 fund-raiser for the Proposition 8 legal fund at the Mandarin Oriental Hotel in New York, organized by, among others, Wall Street financiers and the former chairman of the Republican National Committee.
“I knew literally no one in the room,” said Mr. Griffin, whose fund-raising activities on behalf of the Obama campaign helped earn him a seat at President Obama’s table at the state dinner at the White House last week. “It was a very bizarre moment for me. It was really a turning point.”
Money does not always translate into political success, of course. While the network has bankrolled the legal case that led two courts to throw out Proposition 8 and also helped power a same-sex marriage bill to law in New York State, tough battles may lie ahead with marriage initiatives on five state ballots this year: Maine, Maryland, Minnesota, North Carolina and Washington.
And opponents say that while they might be outmatched financially — the National Organization for Marriage said it had an annual budget of about $20 million, and estimates that the combined money being spent in support of same-sex marriage is many times that — they have a more saleable message. Brian S. Brown, the president of the organization, said voters had opposed same-sex marriage in the 30 times the question has been on a ballot since 2000.
“We know what we have to do to win,” he said. “We have shown we did not need to match them dollar for dollar. I would love to. But we’ve won without doing that.”
The seed money collected at the Geffen home — part of millions of dollars that have flown into campaigns to finance court battles, initiative efforts and the campaigns of sympathetic state lawmakers — was an early indicator of the changing donor network. Mr. Geffen is gay; Mr. Bing is straight. Mr. Bing is known as a big contributor to political causes, but associates said this was only the second time he had ever made a major contribution to a gay-related cause.
The Republican support for the effort largely began after Mr. Olson, a solicitor general under President George W. Bush, lent it his name. It accelerated with the fund-raising role of Ken Mehlman, the former chairman of the Republican National Committee and of Mr. Bush’s re-election campaign, who announced he is gay 18 months ago and has since helped raise close to $3 million by fishing in waters where gay organizers had rarely gone before.
As surprising — and encouraging — to organizers of the movement are the Wall Street names added to their roster. Prominent among them is Paul Singer, a hedge fund manager who is straight and chairman of the conservative Manhattan Institute. He has donated more than $8 million to various same-sex marriage efforts, in states including California, Maine, New Hampshire, New Jersey, New York and Oregon, much of it since 2007.
“It’s become something that gradually people like myself weren’t afraid to fund, weren’t afraid to speak out on,” Mr. Singer said in an interview. “I’m somebody who is philosophically very conservative, and on this issue I thought that this really was important on the basis of liberty and actual family stability.”
The New York fund-raiser was sponsored by Mr. Singer and Mr. Mehlman, among others, and drew a crowd that included Henry R. Kravis, a private equity investor; Daniel S. Loeb, a hedge fund manager; Lewis M. Eisenberg, a former finance chairman for the Republican National Committee; and Steve Schmidt, who managed the 2008 presidential campaign of Senator John McCain.
“I try to look for places where there is both a financial and political angle,” Mr. Mehlman said. “So the fact that we were able to get prominent Republicans and businesspeople, some of whom were involved before but others who are new, helped in the effort both financially and politically.”
This is on top of a network of wealthy gay men and women who have a history of giving money to philanthropic causes and in recent years have shifted much of their effort to same-sex marriage.
Tim Gill, a billionaire software developer from Colorado, who is gay, has assembled a network that has been likened to a gay version of Emily’s List, which supports female candidates. Mr. Gill’s foundations have distributed over $235 million to gay-related causes, with much going to promote same-sex marriage, his advisers said.
“My husband and I are legally married in some states but obviously not married in others, so that’s a pretty big focus,” Mr. Gill said.
David Bohnett, a co-founder of GeoCities and a gay philanthropist here, has donated more than $4 million over the past 10 years to candidates and organizations supporting same-sex marriage, his advisers said.
And this week, Freedom to Marry, a group that advocates same-sex marriage, announced on Thursday a $3 million fund-raising campaign aimed at winning the five ballot initiatives and pushing the New Jersey Legislature to override the veto by Gov. Chris Christie of a same-sex bill, said Evan Wolfson, the founder of Freedom to Marry.
The first $250,000 is coming from Chris Hughes, a founder of Facebook, and his fiancé, Sean Eldridge. “Chris and I certainly prioritize in our contributing,” Mr. Eldridge said. “Marriage is a top priority.”
Mr. Brown said the same-sex-marriage cause had been greatly helped by people like Mr. Hughes. “A couple of billionaires go a long way,” he said. But Mr. Wolfson said the “vast majority” of donations came from small donors.
The broadening of the coalition also reflects a concerted effort by backers of same-sex marriage to put straight and Republican supporters out front. “Prominent straight people from entertainment were crucial,” said Dustin Lance Black, an Oscar-winning screenwriter who wrote “8,” a play re-enacting the courtroom challenge to Proposition 8. “We wanted people who were not the usual suspects.”
A reading of Mr. Black’s play here, which raised more than $2 million, was notable for the participation of screen idol-type American actors like George Clooney and Brad Pitt, who historically would have steered clear of this kind of production. Norman Lear, the television producer, wrote a $100,000 check even before Mr. Geffen had made his commitment. “It was the right moment and the right way to go,” he said.