J.E. "Bud" Clark, the tavern owner who staged a stunning upset when he won election as mayor of Portland, Ore., six years ago, has decided not to seek a third term in 1992.

The unconventional Clark, who rides to work on a beat-up bicycle, uses a pocket camera to snap pictures of people who drop by city hall and shouts "Whoop, Whoop" everywhere he goes, is credited with bringing a common-sense approach to city problems.

The 59-year-old Democrat made the announcement on his weekly cable television show. He said passage of Measure 5, a tax-limit initiative, by Oregon voters in November was a deciding factor.

"I cannot realistically make the tough decisions required to manage the budget process over the next two years, hold the council accountable to the public interest and also be a candidate for political office," Clark said. "There already has been too much speculation about who will run for mayor and not nearly enough tough debate about the services this city should provide in the wake of Measure 5."

Clark was given little chance of winning the nonpartisan post in 1984 when he challenged incumbent Frank Ivancie (D), who ran an advertisement deriding Clark. "We all like a good joke," the ad stated. "But Portland's future is at stake. Do you want to put a self-proclaimed born-again pagan in the mayor's office, someone whose chief claim to fame is exposing himself to a downtown statue?"

Clark had appeared in an "Expose Yourself to Art" poster, which sold more than 300,000 copies nationally. It pictures Clark, back to the camera, in a raincoat that he is flashing open toward a statue of a nude female.

After his victory, Clark attracted the kind of national attention most politicians only dream about, including invitations to appear on the Johnny Carson and David Letterman television shows.