This episode's headline: U.S. Shelling Backs Lebanese Army; Down's Syndrome. The guests include MICHAEL DUNN, Defense Journalist; HAROLD SAUNDERS, American Enterprise Institute; Sen. PAUL TSONGAS, Democrat, Massachusetts; Rep. DUNCAN HUNTER, Republican, California. Byline: In New York: ROBERT MacNEIL, Executive Editor; In Washington: JIM LEHRER, Associate Editor; Reports from NewsHour Correspondent: TAMRA THOMASSON, Portland, Oregon; Videotape Courtesy of Oregon Public TV: LESTER M. CRYSTAL, Executive Producer