Three Republicans on the Health, Education, Labor and Pensions Committee voted for the bill, which supporters hope will improve its chances to pass the Senate with the 60 votes it will need.
Four Republican senators — Orrin G. Hatch of Utah, Lisa Murkowski of Alaska, and Mark S. Kirk of Illinois, who voted for it in committee, along with Susan Collins of Maine, one of the bill’s sponsors — are now on record supporting the bill, which has been debated in one form or another for more than a decade in Congress but has never passed the Senate.
Supporters said they were emboldened by the 15-to-7 vote on Wednesday and took it as yet another sign, after last month’s Supreme Court decision invalidating the Defense of Marriage Act, that gay rights are on an inexorable climb.
But the political reality in Congress means the fate of the legislation is very much in doubt, despite the ease with which it cleared the committee. Even if the bill garners the necessary 60 votes to pass the Senate — not a sure thing, even with the support of the four Republicans, as three Democrats remain uncommitted — it faces an almost certain death in the House, where the Republican leadership has no plans to bring it up.
“I wouldn’t underestimate the difficulties of getting the bill through the whole Congress,” said Mr. Kirk shortly after the vote, which happened so quickly it surprised even some of the senators on the committee. It was less than 20 minutes from the time the meeting was gaveled in to the time it adjourned.
Senator Tom Harkin, Democrat of Iowa and the committee’s chairman, noted the irony of approving a measure that had languished for so long.
“It has been a long time coming,” Mr. Harkin said. “And sometimes you work on these things for years and years. And all of a sudden it passes.”
Mr. Kirk has long supported the legislation. And Ms. Murkowski was seen as a likely yes after she became the third Senate Republican to express support for same-sex marriage last month.
She said Wednesday that hearing from her constituents over the July 4 recess ultimately helped put her over the edge. “When I was home over the break, I think it was 1,774 postcards were delivered to my office from Alaskans around the state,” she said. “It’s important to them. It’s important to me.”
But the “yes” vote from Mr. Hatch, a Mormon, came as something of a surprise. Like many conservatives, including some of the seven who voted “no” on Wednesday, Mr. Hatch said he was concerned that religious institutions could be penalized. But the way the legislation is written, religious organizations like houses of worship, schools and missions are exempt from the law, as is the military and small businesses with fewer than 15 people.
Similar legislation has faltered in Congress before. The most problematic aspect in the past had been the inclusion of transgender people. When former Representative Barney Frank, Democrat of Massachusetts, introduced the bill in the House in 2007, he ultimately agreed to remove the transgender provision, helping to ensure its passage.