SEATTLE — Washington appeared almost certain to become the seventh state to allow same-sex marriage after the State Senate voted late Wednesday for a measure that would allow gay and lesbian couples to marry beginning this summer.

Supporters had considered the Senate to be the more challenging chamber in which to pass the bill, but it was approved easily, by a vote of 28 to 21, after less than 90 minutes of debate. The measure now moves to the House, where it has wide support and could be voted on as soon as next week. Gov. Christine Gregoire has urged the bill’s approval. The governor is a Democrat, and both legislative chambers are controlled by Democrats.

“Regardless of how you vote on this bill, an invitation will be in the mail,” Senator Ed Murray of Seattle, the prime sponsor in the Senate, said in his final remarks before the vote. Mr. Murray, who is gay, has noted many times publicly that he and his longtime partner hope to marry in their home state.

The measure, echoing one passed in New York last June, includes language assuring religious groups that they would not be required to marry same-sex couples or allow them to marry in their facilities. Washington would join New York, Massachusetts, Connecticut, New Hampshire, Vermont and Iowa as states where same-sex couples can marry. Washington, D.C., also allows same-sex marriage.