This episode's headline: Calling It Quits; Challenging Marcos; Soviet-American Television. The guests include In Washington: LAURENCE BARRETT, Time Magazine; ZBIGNIEW BRZEZINSKI, Former National Security Adviser; In Manila: CORAZON AQUINO, Philippines Presidential Candidate; Reports from NewsHour Correspondents: MARY ANNE KANE, in Boston; JUNE CROSS, in Washington; FRED SAM LETHEROW, in Minneapolis. Byline: In New York: CHARLAYNE HUNTER-GAULT, Correspondent; In Washington: JIM LEHRER, Associate Editor