This episode's headline: After the Fall; Crack Down; Lasting Impression; Searching for Peace. The guests include PRES. ALFREDO CRISTIANI, El Salvador; SALVADOR SANABRIA, FMLN Spokesman; CORRESPONDENTS: CHARLES KRAUSE; TOM BEARDEN; ESSAYIST: AMEI WALLACH. Byline: In New York: ROBERT MacNeil; In Washington: JAMES LEHRER