Robert A. dePalma, 56, vice chairman of the board of directors of Rockwell International Corp. and chief financial officer of the aerospace firm from 1976 to 1991. He joined Rockwell in 1970 as assistant treasurer and had been a company director since 1986. Before joining Rockwell, dePalma was a vice president with Pittsburgh National Bank in Pennsylvania. In college he was captain of the Duquesne University basketball team and an All-American in 1957. In Pittsburgh on Tuesday of what the company described only as a long illness.