Washington state Senator Jim Kastama of Puyallup will declare his position on a gay marriage bill at a Thursday news conference, the AP reported.

Kastama is among the half-dozen lawmakers who remain undecided on the proposed measure.

The bill, which was formally introduced in the Senate last week, would make Washington the seventh state to legalize gay marriage after New York, Massachusetts, Iowa, Connecticut, Vermont and New Hampshire. Gay couples may also legally marry in the District of Columbia.

The measure is expected to clear the House with ease and Governor Chris Gregoire pledged her support during a press conference earlier this month.

But supporters remain 2 votes shy of passage in the Senate, making Kastama's announcement critical.

Washington state currently recognizes gay couples with domestic partnerships. A 2009 expansion of the law gave gay couples all the protections of marriage. A ballot initiative to repeal the law failed.

In 1998, Kastama, a conservative Democrat, voted in favor of a bill that defines marriage as a heterosexual union. However, eleven years later he supported expanding the state's domestic partnerships law.