The fascination about the story of Alex Kelly -- the Darien, Conn., pseudo-preppy who fled the country eight years ago to escape two rape charges and is on trial again, following a recent mistrial -- has already lent itself to much media coverage, including an evocative essay by Susan Cheever in the New York Times Magazine. Now it appears at least two publishers are at work on books about the case: next spring Donald I. Fine will publish The Trial of Alex Kelly by Darien native Samuel A. Schreiner, who is covering the trials; and Pocket Books hopes to publish Sheila Weller's book on the case as soon as Labor Day. Weller, author of Raging Heart, the Pocket bestseller on Nicole Simpson, is conducting many interviews with former friends of Kelly's and is calling her book Saint of Circumstance, because "you can't write a book about people who were teenagers in Darien in the '80s and not name it after a Grateful Dead song."