The Washington state Legislature has enough votes to pass legislation legalizing same-sex marriage.

OLYMPIA — Gay-marriage supporters Monday may have clinched the votes needed to pass a bill through the Legislature, but opponents said the fight’s far from over.

“It’s not done. In fact, it’s just started,” said Joseph Backholm, executive director of the Family Policy Institute of Washington, vowing that legalization of same-sex marriage would end in a referendum challenge.

The marriage bill received a big boost Monday when state Sen. Mary Margaret Haugen, D-Camano Island, became the 25th senator to announce her support, issuing the endorsement during a whirlwind day of packed hearings on the legislation and a rally by opponents.

Haugen’s decision apparently secures passage in the Senate, while the state House already has enough lawmakers signed on to approve it. Gov. Chris Gregoire backs the bill as well.

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If it passes, gay and lesbian couples in Washington could get married starting in June. But a successful referendum drive would prevent the bill from becoming law until voters decided the issue in November.

There would be no window of opportunity for gay marriages before the election, according to the Secretary of State’s Office.

The Senate measure is expected to be voted out of committee by Thursday, but it’s unclear when it would go to a floor vote.

Sen. Ed Murray, D-Seattle, prime sponsor of the legislation in the Senate, said there’s an off chance a vote could happen late next week, but it likely would occur later in the session.

It’s also unclear which group, or coalition of organizations, may take the lead on a referendum challenge.

“Those discussions are taking place,” Backholm said. “Who’s leading it, I don’t know how to answer it at this point.”

A referendum cannot be filed until the governor signs the legislation.

Under state law, opponents have 90 days from the end of the session to collect 120,577 signatures to put a referendum on the ballot. The regular session ends March 8.

If opponents turn in enough signatures, the law would be put on hold until the election. If upheld by voters, the law then would go into effect Dec. 6.

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

But no state has ever approved gay marriage at the ballot. In only one, Maine, have voters been asked to rescind a same-sex marriage law approved legislatively. In 2009, six months after the Maine Legislature passed that state’s same-sex marriage law and the governor signed it, residents voted by a margin of 53-47 to repeal the law.

“Emotional moment”

Support for gay marriage has been building since lawmakers and advocates announced in November they would push the legislation this year. Identical gay-marriage bills were later introduced in the House and Senate.

Microsoft and several other prominent Pacific Northwest businesses endorsed the legislation last week, and Jim Kastama, a conservative Democrat from Puyallup who once opposed same-sex marriage, said he now will vote for it.

Still, Murray had thought he’d have to put the legislation up for a vote without knowing the outcome.

That changed Monday morning when Haugen came to his office to visit him and his longtime partner, Michael Shiosaki.

“We’ve been talking about this issue for years,” Murray said of Haugen. “I knew she was struggling with it. We’ve had some serious conversations. She came in this morning and talked to Michael and me and told us her decision … It was a surprising and emotional moment for all three of us.”

Haugen said Monday night that a provision in the legislation that says churches wouldn’t be required to perform marriage services for gay and lesbian couples was an important factor in her decision. She added that she spent a lot of time listening to people in her district.

“I prayed a lot about this. I was at peace after I made the decision, but it helps to move on,” she said. “There are so many issues this session that are so important, from education to taking care of old people to transportation. We had to move off this issue. I was finding myself absorbed constantly about this issue.”

Haugen has been in the Legislature since 1983 and moved to the Senate in 1993. She chairs the Senate Transportation Committee and primarily is known for strong stances on transportation policy including the state ferries system — not social issues.

She has stressed that she represents a diverse district with divided views on gay marriage. The district in 2009 narrowly approved Referendum 71, the “everything but marriage” law, by a margin of about 51 to 49 percent.

She said her preference would be to send the issue to voters to decide, but there isn’t support in the Legislature to do that.

Uncommitted legislators

Murray said he now believes he might get more than 25 votes for his bill.

So far, 23 Democrats and two Republicans in the Senate have pledged support the measure.

State Sens. Andy Hill, R-Redmond; Joe Fain, R-Auburn; Paull Shin, D-Edmonds; and Brian Hatfield, D-Raymond, are uncommitted, according to the lawmakers or members of their staffs.

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

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

Although gay marriage never has won at the ballot box, several recent polls in Washington and nationally have left supporters encouraged.

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

Information from The Associated Press is included in this report.

Andrew Garber: 360-236-8267