This episode's headline: Newsmaker; Defining the Mission Conversation p Playing Beethoven. ANCHOR: JIM LEHRER; GUESTS: AMBASSADOR ROBERT BUTLER, Chief U.N. Weapons Inspector; SEN. JOSEPH LIEBERMAN, [D] Connecticut; SEN. JOHN WARNER, [R] Virginia; ROBERT HUNTER, Former U.S. Ambassador to NATO; MICHAEL MANDELBAUM, Johns Hopkins University; ANNE-SOPHIE MUTTER, Violinist; CORRESPONDENTS: ELIZABETH FARNSWORTH; PHIL PONCE; KWAME HOLMAN