Washington Gov. Jay Inslee said the crew of the plane was serving the nation.
"I know all Washingtonians join me in sending condolences to the crew's families and to their fellow service members," Inslee said.
U.S. Sen. Patty Murray, D-Wash., also said her prayers were with family members of the crew.
The crash occurred in a rural area between the towns of Harrington and Odessa, about 50 miles west of Spokane. Aerial views of the crash site showed a large crater in a farm field, surrounded by blackened vegetation. Much of the plane appeared to have disintegrated on impact.
"You could see smoke and bits of plane in the middle of the field," local resident HaLee Walter told KREM-TV after visiting the crash site.
The Prowler specializes in electronic warfare such as jamming enemy radar and intercepting radio transmissions. It can also be equipped with missiles.
Whidbey Island officials said the plane that crashed was attached to Electronic Attack Squadron VAQ-129.
Associated Press writer Donna Cassata in Washington, D.C., contributed to this report.