OLYMPIA — Gov. Chris Gregoire will break her silence on an effort to legalize same-sex marriage in Washington state.

Gregoire has invited sponsors of the soon-to-be introduced bill to Olympia for a Wednesday news conference on the issue. Gregoire has long supported the state’s domestic partnership laws but has not yet given a firm signal on whether she supports same-sex marriage.

Spokeswoman Karina Shagren refused to provide details Tuesday after saying the governor will be addressing marriage equality.

Lawmakers will return to the Capitol on Monday for the start of a 60-day legislative session, and Democratic Sen. Ed Murray of Seattle said he expects a bill to legalize same-sex marriage to be introduced next week.

Murray, a gay lawmaker who has spearheaded past gay rights and domestic partnership laws in the state, said the underlying domestic partnership law has helped lay the groundwork for full marriage.

If Gregoire publicly supports the measure on Wednesday, “it would certainly help us move the issue of marriage equality forward this session,” he said.

In November, a coalition called Washington United for Marriage announced it would lobby the Legislature to approve a gay marriage measure this year.

The state’s underlying domestic partnership law, which the Legislature passed in 2007, provided hospital visitation rights, the ability to authorize autopsies and organ donations, and inheritance rights when there is no will. Under state law, senior couples can register as domestic partnerships as well.

In 2009, the Legislature passed, and voters later upheld, a bill that greatly expanded those rights and was known as the “everything-but-marriage” bill. Nearly 19,000 people in Washington are registered as domestic partners.

Same-sex marriage is legal in Connecticut, Iowa, Massachusetts, New Hampshire, New York and Vermont, as well as the District of Columbia. Several other states, including Washington, have laws that either recognize civil unions or domestic partnerships.

While most marriage rights are covered under the existing partnership law, supporters say the push for marriage is still necessary.

Rep. Jamie Pedersen, a Seattle Democrat who has been a main sponsor on the domestic partnership bills in the House, said that a marriage law in Washington would allow for reciprocity of recognizing rights if a same-sex couple travels to other states that already have marriage laws.

Aside from that, he said that the social element is important as well.

“There is the question of the fairly deep meaning of the word ‘marriage’ in people’s psyche,” he said.