This episode's headline: Election Preview; Campaign '96 - Reading the Numbers; Ad Wars; Political Wrap. ANCHOR: JIM LEHRER; GUESTS: ROBERT GALLUCCI, Former State Department Official; WARREN ZIMMERMAN, Former Ambassador to Yugoslavia; ANDREW KOHUT, Pew Research Center; KATHLEEN HALL JAMIESON, University of Pennsylvania; MARK SHIELDS, Syndicated Columnist; PAUL GIGOT, Wall Street Journal; CORRESPONDENTS: ELIZABETH FARNSWORTH; GABY RADO; MARGARET WARNER;