As Klinger in "M*A*S*H," Jamie Farr did everything to get out of the Army and to stay away from anything that smacked of official Washington. The only member of the "M*A*S*H" cast to have actually served in Korea, Farr will be in town this week for a U.S. Savings Bonds rally, in which he will be appointed honorary chairman of the federal government's 1985 Savings Bonds campaign. The appointment will be made by the campaign's federal chairwoman, Margaret M. Heckler, secretary of health and human services . . .

Sen. Paul Simon is taking advantage of Mardi Gras as the theme for his first Washington fundraiser tonight at Prospect House. The $500-a-plate pre-Lent party to help pay off the Illinois Democrat's campaign debts is expected to attract some of the party's stars, including Sens. Edward M. Kennedy, Gary Hart, Frank R. Lautenberg and Howard M. Metzenbaum . . .

John Clark Gable, the son whom Clark Gable never knew, was married over the weekend. The 23-year-old Gable (whose legendary father died of a heart attack four months before his birth) married Tracy LaRae Yarro, a beautician and daughter of a wealthy California real estate broker. Gable, a professional auto racer, is little known to the public, even though his birth made international news, including the cover of Life magazine. His mother, Kay Williams Spreckels Gable, was Gable's fifth wife and was 42 years old when John Clark Gable was born. She died in 1983 . . .

Jack Valenti, the head of the Motion Picture Association of America, has a job that takes him to some of the best neighborhoods. Last week, he headed a delegation of television executives in Monte Carlo and paid a visit to the Royal Palace to talk with Prince Rainier. The prince, Valenti says, is a consummate movie buff who "asked penetrating questions about every phase of the business. I was very impressed" . . .