7PM This episode's headline: Iran-contra Hearings; Costa Rica Dead Beat/Truce?. The guests include In New York: JOHN LYONS, Bank Analyst; In Boston: JEFFREY SACHS, Harvard University REPORTS FROM NEWSHOUR CORRESPONDETNS: JUDY WODRUFF, LEE HOCHBERG, KCTS, Seattle. Byline: In New York: ROBERT MacNEIL, Executive Editor; In Washington: JIM LEHRER, Associate Editor GUESTS: In New York: JOHN LYONS, Bank Analyst; In Boston: JEFFREY SACHS, Harvard University REPORTS FROM NEWSHOUR CORRESPONDETNS: JUDY WODRUFF, LEE HOCHBERG, KCTS, Seattle