This episode's headline: What Should be Secret?. The guests include JACK MAURY, Association of Former Intelligence Agents; MORTON HALPERIN, Center for National Security Studies; Sen. JAKE GARN, Republican, Utah; Rep. GLENN ENGLISH, Democrat, Oklahoma. Byline: In New York: ROBERT MacNEIL, Executive Editor; In Washington: JIM LEHRER, Associate Editor; DAN WERNER, Producer; JUNE CROSS, ANNETTE MILLER, Reporters