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.