William E. Ahearn, managing editor of The Associated Press, was appointed executive editor Tuesday, to succeed Walter R. Mears, who will become Washington vice president and a political columnist for the news cooperative. President Louis D. Boccardi announced the appointments, effective Jan. 1, 1989. Ahearn's successor as managing editor will be Martin C. Thompson, who has been AP chief of bureau in Los Angeles. Mears, whose Washington career spanned 23 years before he became executive editor, asked to return to the capital and to the political writing that was his specialty. Boccardi said the change was in line with a plan established when Mears came to New York five years ago. ``He has been a great help to me and an asset to the AP in his time here, and he will continue those contributions from the city that has been his professional home,'' the AP president said. Mears, who won a Pulitzer Prize in 1977 for his political reporting, will write three analytical columns a week for the AP in the new assignment. Charles J. Lewis remains in his post as Washington bureau chief. Boccardi also announced that Charles J. Hanley, who has been assistant managing editor, will become deputy managing editor. Julie Dunlap was named assistant managing editor@features, and Mike Silverman was appointed assistant managing editor@national news. Mears, 53, became executive editor in January 1984, after serving as Washington bureau chief for seven years. He has been an AP special correspondent since 1975 and a vice president since 1978. He first joined the AP in Boston in 1955 while still a Middlebury College student, returned in 1956 and became Montpelier, Vt., correspondent later that year. Mears was reassigned to Boston in 1960 and transferred to Washington in 1961. Ahearn, 45, has been managing editor since 1985. He joined the AP in 1971 in New York as a broadcast news writer after serving with the Army as an infantry officer in Vietnam. Ahearn moved to the New York General Desk, the AP's main news desk, in 1972. He was named enterprise editor in 1979 and assistant managing editor in 1981. He was graduated from the University of Bridgeport in 1965, worked as a copy editor on the Bridgeport Post-Telegram, then attended graduate school at Boston University. Thompson, 50, has been chief of bureau in Los Angeles since 1986. He was chief of bureau in San Francisco for 11 years prior to that. He joined the AP in Seattle in 1966; was named correspondent in Reno, Nev., in 1968; and then transferred to the AP's San Francisco bureau in 1970 where he served as news editor. Thompson joined the AP after serving as a newsman for radio station KEDO in Longview, Wash., and then was news director of radio station KREW in Sunnyside, Wash. Thompson is a 1960 graduate of the University of Washington. Hanley, 41, joined the AP in Albany following graduation from St. Bonaventure University. He transferred to the Foreign Desk in New York in 1976 where he was an editor and a special writer who traveled extensively on foreign assignments. He was named assistant managing editor in 1987. Dunlap, 40, has been the AP's senior feature editor for six years. She joined the AP in Philadelphia in 1974 and transferred to the General Desk two years later. Following a year as an editor at The New York Times, she returned to the AP and became enterprise-special assignments editor with responsibility for AP's six-member regional reporting team and five-member national writing team. She is a graduate of Penn State University. Silverman, 44, joined the AP in San Francisco in 1971 and transferred to the General Desk five years later. In 1985 he was named AP's senior national editor, responsible for coordinating daily coverage of national news. Silverman is a graduate of the University of Chicago and Stanford University.