BELLE HAVEN by Juliet Fitzgerald (Viking: $18.95; 224 pp.). Juliet Fitzgerald, the pseudonymn, we are told, for "an award-winning writer," has dipped into the fount of gothics to create the fabulously opulent Virginia estate of Belle Haven, ruled by villainous but beautiful Charlotte and her crooked lawyer, Eugene. With the arrival of Charlotte's plain but good-natured niece, Dabney, this keg of intrigue, passion and greed explodes. The plot and characters are drawn so broadly, one is unsure whether "Belle Haven" should be read as a true bodice-ripper a la Victoria Holt or Barbara Michaels, or as a satire of the genre. Dabney falls for handsome, young Dr. Bay Hamilton; Charlotte quite literally burns for her sins, and Belle Haven goes the way of the House of Usher. In the final pages, evil is punished and true love is reaffirmed. Does Juliet Fitzgerald have her tongue firmly planted in cheek? And is there a trend of successful novelists like Joyce Carol Oates and Anne Rice slumming pseudonymously?