Entertainer Kenny Rogers and his wife Marianne will distribute $100,000 in cash prizes at the Third Annual World Hunger Media Awards at the United Nations tonight. Among the 20 honorees: best newspaper coverage, Frank Starr and others at the Baltimore Sun; best cartoon coverage, Herblock, The Washington Post; best periodical coverage, Rural Coalition; and honorable mention newspaper coverage, Rick Atkinson of The Kansas City Times, now of The Washington Post . . . Media Movements: Valerie McGhee, a cofounder of the Washington Journalism Review, is leaving Dossier magazine to become an editor at Saturday Review; Wall Street Journal political reporters Robert Merry and Jane Mayer are now covering the White House, replacing Rich Jaroslovsky, who has become feature editor in the Washington bureau . . . Conductor Klaus Tennstedt, who conducted the London Philharmonic here Nov. 3, is suffering from nervous exhaustion and has withdrawn from all performances of "Elektra" at the Metropolitan Opera. On his recent tour with the Philharmonic he conducted 18 concerts in three weeks. He will be replaced by James Levine . . . Those were ducks receiving the royal treatment at the Vista Hotel yesterday. They were the famous Peabody Hotel ducks in town to promote Quest '84, a meeting of planners and exhibitors. And today the ducks are to walk a red carpet to Dominique's restaurant to the strains of the "King Cotton March." They will dine on bean soup, and in their honor, duck will not be served on the menu . . .