SEATTLE (AP) _ Washington voters have set up a showdown between Slade Gorton, a moderate Republican hoping to return to the U.S. Senate, and liberal Democratic Congressman Mike Lowry, making his second try for the Senate.

In other primary results Tuesday, state Rep. Bob Williams, a fiesty, evangelical conservative, upset King County prosecutor Norm Maleng in the GOP governor's race and in November will face incumbent Democratic Gov. Booth Gardner, an early supporter of Michael Dukakis.

U.S. Rep. Don Bonker of Vancouver lost the Democratic Senate nomination to Lowry, his old friend and ally, after a vote tally that was neck and neck for much of the evening.

But when his emotional roller coaster screeched to a halt, his grin gave way to a grimace.

''Too soon it comes to an end,'' Bonker, 51, said in an early morning concession speech in which he pledged to support Lowry and help return to the Democrats a seat long held by Democratic Sen. Henry ''Scoop'' Jackson.

Republican Dan Evans held the seat since Jackson's death in 1983 but elected not to seek a second term.

Evans beat Lowry, 49, for the Senate seat in 1983. Gorton lost his re- election bid to the state's other Senate seat to Democrat Brock Adams in 1986.

With 99 percent of the state's 6,655 precincts reporting, the rumpled, expressive Lowry had 55 percent of the Democratic vote to Bonker's 45 percent. Lowry had 275,840 votes to Bonker's 225,376.

Gorton, 60, a former state attorney general who swept into the Senate on the Reagan landslide of 1980, demolished his lesser known GOP challengers, former state Supreme Court Justice William Goodloe of Seattle and Doug Smith, an Everett attorney and former White House aide.

Gorton took 86 percent of the GOP vote, or 322,270 votes. Smith, who had called Gorton too liberal, was a distant second with 8 percent, or 29,662 votes, and Goodloe had 6 percent, or 24,436 votes.

''I'm just delighted with the showing. I have no question we can do it in November,'' Gorton said in an interview. ''We'e in great shape. Our position contrasts with Mike Lowry on almost every issue.''

Gorton was the top Senate vote-getter of the night, and insisted his tally would have been much higher had not so many crossed over to vote in the more interesting Democratic primary.

Lowry, quickly trying to move to the center politically, told a reporter: ''What I am is a middle-of-the-road candidate with my positions. ... That's how we got the votes: our common sense approach to what this country should be doing.''

Pollsters say the two candidates have perhaps the highest negative ratings of any Washington politicians.

Both candidates tried to polish their images during the campaign. Gorton attempted to warm his icy, aloof demeanor and Lowry toned down his ebullient, arm-waving style and shaved his beard.