The donors represent some of New York's wealthiest and most politically active figures and include Paul E. Singer, a hedge fund manager and top-tier Republican donor, as well as two other financiers, Steven A. Cohen and Clifford S. Asness.

At the same time, Mayor Michael R. Bloomberg, a billionaire businessman and philanthropist who has been a major contributor to Senate Republicans in New York, plans a significant push for same-sex marriage: giving at least $100,000 of his own money, hosting a fund-raiser at an Upper East Side town house, traveling to Albany to lobby lawmakers and giving a speech on the issue.

The new donations represent roughly two-thirds of the same-sex marriage coalition's fund-raising, making New York the rare state where a lobbying campaign in favor of legalizing gay unions is not being financed primarily by liberal donors and Democrats. The support is likely to jolt the traditional financial and political backers of gay rights causes, who now find themselves in the unfamiliar position of being outraised and outspent in New York.