Iowa farm boy Lewis Tater has a brainstorm: instead of continuing the correspondence courses that are learnin'' him to write cowboy novels, he''ll travel to the out-West school itself and soak up the campus atmosphere first hand. He arrives to find the school is a postal box. Write ''em, cowboy. Tater''s adventures don''t stop there in an acclaimed tumbling tumbleweed of a film that has him earning his spurs in the yippie-yi-o of ''30s "B" Westerns, complete with a veteran sagebrusher (Andy Griffith), a savvy script girl (Blythe Danner) and a hilariously inept director (Alan Arkin, the New York Film Critics Award choice as the year''s Best Supporting Actor). Jeff Bridges plays Tater, a likable pilgrim as fresh-faced and innocent as Bridges''s decades-later Rooster Cogburn in True Grit is worn and wise.