WASHINGTON — Rep. Jay Inslee of Washington announced Saturday that he would resign his seat in Congress so that he could focus on his campaign for governor.

Inslee’s resignation will create a third vacancy in the House, all seats held by Democrats.

Former Rep. Gabrielle Giffords, shot in the head last year as she met constituents in Tucson, resigned her Arizona congressional seat in January to focus on her recovery. Last Tuesday, Rep. Donald M. Payne, 77, of New Jersey, died after a battle with colon cancer.

Inslee has represented Washington’s 1st District in Congress since 1999. He also served a term representing the 4th District from 1993 to 1995.

His resignation will take effect March 20.

“I am not one for half-measures or halfhearted efforts,” Inslee said in a statement from his campaign. “I am going to leave everything on the field.”

Inslee is the sole Democrat in the race to succeed two-term Democratic Gov. Chris Gregoire, who chose not to seek a third term this year.

Polls show Inslee trailing two-term state Attorney General Rob McKenna, a Republican.