This episode's headline: Cold War Secrets; China in Transition; Conversation. The guests include HAZEL O'LEARY, Secretary of Energy; BARTON BERNSTEIN, Historian; DR. JACK GEIGER, Medical Researcher; ELLIS COSE, Author; CORRESPONDENTS: ROBERT OXNAM; CHARLAYNE HUNTER-GAULT. Byline: In New York: ROBERT MacNeil; In Washington: MARGARET WARNER