OLYMPIA — The Legislature is on the verge of having enough support to make Washington the seventh state to approve gay marriage, according to a tally by The Associated Press.A same-sex marriage bill is expected to be introduced by the end of the week. The AP reached out to all 49 state senators over the past week and found that more lawmakers are firmly supporting gay marriage than opposing it, by a margin of 22-18.The measure needs 25 votes to pass the Senate. The House is widely expected to have enough support, and Gov. Chris Gregoire publicly endorsed gay marriage for the first time last week.Four Democrats say they are considering whether to support it, including one who is leaning in favor. A pair of Republicans is among those supporting the proposal, and two first-term GOP members said they are still discussing the issue with constituents.Democratic Sen. Ed Murray, a gay lawmaker from Seattle who has for years led efforts to approve same-sex marriage, said that he’s “50 percent optimistic” it will pass. He noted that he saw a gay civil rights measure he spearheaded lose by one vote in 2005 before it passed by a single vote the following year.