OLYMPIA — A House committee on Monday advanced a proposal to legalize same-sex marriage in Washington state, and the Senate is expected to vote on its companion bill within days.

The House Judiciary Committee approved its gay marriage bill on a party line vote, with seven Democrats voting for it, and six Republicans voting in opposition.

Three Republican amendments were rejected, including one that would have added private businesses and individuals, such as bakers and photographers, to the religious exemption in the measure that doesn’t require religious organizations or churches to perform marriages, and doesn’t subject them to penalties if they don’t marry gay or lesbian couples.

Rep. Jay Rodne, R-Snoqualmie, called the bill “an act of raw political power to modify the definition of marriage.”

“There has been no compelling justification to abandon traditional marriage,” he said.

Opponents of same-sex marriage have already promised a referendum battle at the ballot if the Legislature passes the bill and it’s signed into law.

Sen. Ed Murray, a Seattle Democrat who is sponsoring one of the bills, said Monday that he expects a floor vote on gay marriage in the Senate on Wednesday. A Senate committee voted to advance Murray’s bill Friday.

Before last week, it wasn’t certain the Senate would have the support to pass the measure, due to a handful of undecided Democrats. But last Monday, after the first public hearing on the issue, a previously undecided Democratic senator, Mary Margaret Haugen of Camano Island, said she would be the 25th and deciding vote in support of the measure, all but ensuring its passage.

The state House already had secured enough votes to pass the bill, and Democratic Gov. Chris Gregoire publicly endorsed the proposal earlier this month.

The House bill is set to advance to a fiscal committee, but a date for a hearing has not been set.

If a marriage bill is passed during this legislative session, gay and lesbian couples will be able to be wed starting in June unless opponents follow through on their threat to file a referendum to challenge it.

A referendum can’t be filed until after the bill is passed by the Legislature and signed into law by Gregoire. Opponents then must turn in 120,577 signatures by June 6.

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

Washington state has had a domestic partnership law since 2007 and an expansion of the domestic partnership law since 2009.

Rep. Jamie Pedersen, D-Seattle, and sponsor of the House bill, said that even though the state’s domestic partnership law has increased rights to gay and lesbian couples, lawmakers have continued to hear from people “whose families have been disadvantaged because they do not have the rights of civil marriage afforded to them.”

Under the bills being considered by the Legislature, couples currently registered in domestic partnerships would have two years to either dissolve their relationship or get married. Domestic partnerships that aren’t ended prior to June 30, 2014, would automatically become marriages.

Domestic partnerships would remain for senior couples where at least one partner is 62 years old or older.