When Clark Gable died in 1960 at 59, there were rumors that his heart attack was caused by the physical stress of shooting horse scenes for "The Misfits" (★★★) in the Nevada desert heat. His trials were compounded by the erratic, let-'em-wait moods of co-star Marilyn Monroe and director John Huston's battle with alcohol. And yet there's a haze of doomed, elegiac romance about this production that gives it a special place in American film history. Arthur Miller wrote the sad-cowboy script for Monroe, his wife, giving her a showcase role as a fragile nature spirit among modern-day stockmen who wrangle mustangs for dog meat. Gable is a tender, stoic hand at the end of the line, and Montgomery Clift, Eli Wallach and Thelma Ritter add pungent support. (7 p.m. Mon., $8, Riverview Theater, 3800 42nd Av. S., Mpls.)