WASHINGTON — Motion Picture Assn. of America president Jack Valenti is set to meet with Argentina’s President Carlos Menem Wednesday in an effort to win greater access to South American market for U.S. films.Among the barriers are Argentine taxes on U.S. film receipts. Other items on the agenda include antipiracy efforts and international copyright protection treaties. Valenti will also attend the Mar del Plata Film Festival today and tomorrow. During the fest, Valenti expects to meet with members of the South American production community.