This episode's headline: Dam That River; Political Wrap; Yen For a Change; Trade- Off; Questionable Perspective. The guests include MARK SHIELDS, Syndicated Columnist; VIN WEBER, Republican Consultant; CORRESPONDENTS: ELIZABETH BRACKETT; AMEI WALLACH; LINDSAY TAYLOR; PAUL SOLMAN. Byline: In New York: ROGER MUDD; In Washington: JAMES LEHRER