When Sen. Daniel J. Evans (R-Wash.) announced last month that he will not seek reelection, it looked as though the state's entire Democratic congressional delegation would run for the seat -- with the exception of House Majority Leader Thomas S. Foley. But it appears that only Reps. Mike Lowry and Don Bonker will run. Rep. Al Swift, who had said he'd run no matter what Evans decided to do, has had a change of heart with Evans out of the race. Swift said he does not want to campaign against fellow Democrats and conceded that he probably could not win the primary. While Rep. Norman D. Dicks "is keeping his options open, the betting line is that he won't do it," said one Washington state source.

Bonker has opened campaign offices, formed a 33-member campaign committee and captured the endorsements of Seattle Mayor Charles Royer and the speaker of the state House, Joe King. But it is the outspoken and flamboyant -- and more liberal -- Lowry who political observers say is the early front-runner for the nomination. Lowry, who ran against Evans in the 1983 special election with the slogan, "Not Just Another Pretty Face," has the most name recognition, according to a recent Democratic poll.

Topping the list of possible GOP candidates, Rep. Sid Morrison has formed an exploratory committee. But his support of the Hanford nuclear reservation project could hurt him as it hurt then-Sen. Slade Gorton (R-Wash.) last year.

Other Republicans being mentioned include Rep. Rod D. Chandler, former governor John Spellman and state party Chairman Jennifer Dunn, a strong conservative. While former Environmental Protection Agency chief William D. Ruckelshaus wants his name off the list, his wife, Jill, a member of the Civil Rights Commission until she was bumped by President Reagan for her liberal views, is being considered.