Tall, imposing American nightclub comedian turned television comic and talk show host, whose shock of thick hair, wide eyes, protruding chin and artful comic style have helped make him one of the busiest and most recognizable performers in TV entertainment during the 1980s and 90s. First and foremost, Leno is a sly but determinedly clean-cut chronicler of American follies and foibles--on a proposed Congressional pay raise, for example, he made a suggestion quoted on the national nightly news: "They say if we give them a 50 percent pay increase they'll stop outside speaking engagements. Maybe