The Washington state House of Representatives was expected to endorse gay marriage on Wednesday in a vote that would move the state another step closer to becoming the seventh to recognize same-sex nuptials.
Floor debate was scheduled to begin in the afternoon, with supporters and opponents predicting the measure would win House passage by at least as comfortable a margin as it took to clear the Senate, on a 28-21 vote, a week ago.
Democrats, accounting for the lion's share of support for the bill, control both legislative bodies but enjoy a bigger majority in the House. Proponents were hoping to stave off any 11th-hour House floor amendments that would force the bill back to the Senate for final passage and thus slow its momentum.
Governor Christine Gregoire, a Democrat in her final year in office, set the stage for swift passage of the measure when she announced last month that she was backing the legislation.
Six other states already recognize same-sex marriage -- New York, Massachusetts, Connecticut, Vermont, New Hampshire and Iowa -- as does the District of Columbia.
Supporters are pushing similar statutes in Maryland and New Jersey, and a referendum to legalize gay marriage in Maine has qualified for the November ballot there.
Gay rights advocates won another victory on Tuesday when a federal appeals court declared a voter-passed ban on same-sex marriages in California to be unconstitutional.
Once the Washington state bill reaches Gregoire's desk, she would have five days, not including Sunday, to sign it into law. It is a timetable that some speculated would lead to its enactment next Tuesday, Valentine's Day.
Still, the measure would not take effect before June 7, three months after the conclusion of the legislative session.
In the meantime, opponents of same-sex matrimony said they would seek to overturn the legislation via one of two ballot measures -- a referendum for repeal or an initiative defining marriage as the exclusive domain of heterosexual couples.
The former would need 241,153 signatures of registered voters by July 6 to secure a place on the November ballot. The latter would need just half the number of signatures by June 6.
If a referendum qualifies for the November ballot, the gay marriage law would be suspended until the election and certification of returns, meaning December 6, before it is either repealed or goes into effect.
Under the initiative process, by contrast, gay marriages could proceed on June 7, regardless of ballot-qualification efforts. But it was unclear whether gay weddings performed in the interim would be nullified if an initiative restricting marriage to male-female unions only were to pass in November.
There is precedent in California for handling such a situation. California's Supreme Court legalized gay marriage in 2008, only for voters to approve a state constitutional amendment banning same-sex matrimony six months later.
The state's high court later upheld the gay marriage ban, known as Proposition 8, but ruled that 18,000 same-sex weddings officiated between May and November 2008, were still legal.
A federal judge later ruled Prop 8 unconstitutional, a decision upheld on Tuesday by the 9th U.S. Circuit Court of Appeals.
Legal experts said that ruling, while narrowly tailored to California, could ease the way for a successful court challenge in Washington state should voters there overturn a gay marriage statute.