OLYMPIA, Wash. — Democratic state Sen. Mary Margaret Haugen announced Monday that she supports gay-marriage legislation in Washington state’s Senate, giving proponents the 25 votes needed for passage.

The state House already has enough lawmakers in support of the measure to approve it. Washington Gov. Chris Gregoire backs the bill as well.

Democratic state Sen. Ed Murray, prime sponsor of the measure in the Senate, had thought he would have to put the legislation up for a floor vote without knowing the outcome.

That all changed Monday.

“I know this announcement makes me the so-called 25th vote, the vote that ensures passage. That’s neither here nor there. If I were the first or the seventh or the 28th vote, my position would not be any different,” Haugen said in a statement.

“I happen to be the 25th because I insisted on taking this much time to hear from my constituents and to sort it out for myself, to reconcile my religious beliefs with my beliefs as an American, as a legislator, and as a wife and mother who cannot deny to others the joys and benefits I enjoy,” she added. Haugen said her preference would be to send the issue to voters to decide, but there aren’t the votes in the Legislature to do that.

Murray praised Haugen as courageous, noting her district is divided politically.

“This was a very difficult decision for her to make, personally and politically,” he said. “These were heart-to-heart discussions and she worked through her own process.”

The announcement comes on the same day that supporters and opponents of gay marriage packed hearings on the legislation in the state House and Senate.

Murray testified in the Senate Government Operations, Tribal Relations and Elections Committee that he had been waiting for 17 years for a chance to ask the Legislature to legalize gay marriage.

“Ultimately,” he said, “this bill is about people who love and cherish each other and wish to honor that commitment through marriage.”

Opponents have vowed to challenge legalization of same-sex marriage at the ballot.

“This is so much more than a legal debate,” Joseph Backholm, with the Family Policy Institute of Washington, testified at the hearing, arguing it should go to voters. “The institution of marriage does not belong to the Legislature. It belongs to the people.”

The National Organization for Marriage on Monday pledged its support to help mount a referendum campaign. The same group last week announced it would spend $250,000 in Washington state to help defeat any Republican who supports the bill.

Several polls show a majority of people in Washington as well as the nation support same-sex marriage.

A poll conducted in October by University of Washington associate professor Matt Baretto showed that 55 percent of voters in Washington would preserve same-sex marriage in a referendum if it appeared on the ballot.

So far, 23 Democrats and two Republicans in the state Senate have said they will vote for the bill.

Republican state Sens. Andy Hill and Joe Fain, as well as Democratic state Sens. Paull Shin and Brian Hatfield are uncommitted, according to the lawmakers or members of their staffs.

Republican state Sen. Doug Ericksen has declined to comment, but records show he has opposed every gay-rights bill that’s come up for a vote in the past.

Once the hearings are over, the bills could move out of committee by Thursday in the Senate and by Jan. 30 in the House. The chairmen of both committees said they have the votes they need. The House bill is also expected to go through the House Ways and Means Committee. It’s not clear if the Senate’s measure will go through Senate Ways and Means.

In the United States, same-sex marriage is legal in New York, Connecticut, Iowa, Massachusetts, New Hampshire, Vermont and the District of Columbia.