This episode's headline: Exxon - Slip-Sliding Away?; Portrait of an Art Critic; Forever Blue. The guests include LEE RAYMOND, Exxon Corporation; DENNIS KELSO, Alaska Environmental Commissioner; WENDY LUERS, National Endowment for the Arts; REP. DICK ARMEY, [R] Texas; CORRESPONDENT: KWAME HOLMAN; ESSAYIST: CLARENCE PAGE. Byline: In Washington: JAMES LEHRER; In New York: CHARLAYNE HUNTER- GAULT