For more than 30 years, Harvey Pekar has been writing comics based on his life in Cleveland, collaborating with R. Crumb and other top illustrators and winning an international cult following. ''American Splendor,'' a movie based on his life and work, was the surprise hit of this year's Sundance Film Festival, where it won the Grand Jury Prize. The film went on to take top honors at Cannes and other festivals. The movie will open in U.S. theaters through August and September. We asked Pekar to recount his long journey to the big screen. This is the first feature-length comic he has ever published in a national magazine.