Somewhere there's heaven/ How high the moon."" You'll remember that one, and you'll have learned the lyrics by heart by the time you're through with this orchestration of the lives of Tudi Taylor, who's gone from G-string to singing stardom, and Don Vestry, an also-ran writer who has spent eight years hacking away in Hollywood to support a vicious, lubricious wife and two children. Tudi and Don meet in the Catskills--background music of kasha and ""struddel""--where Don has come to do her life story as a novel. Tudi won't agree, nor will she accept the fact that they're both losers but could make it together. When last seen, Tudi is doing cruises, and Don has indeed written that novel--which is better than anything he or anybody else anticipated. Rogers' novel isn't; it goes on at unconscionable length without ever quite making up its mind what matters most--sex or sentiment. After all, what can you hope for if the moon is no higher than a neon name on a marquee?