THE BLACK SEA by Richard Setlowe (Ticknor & Fields: $21.95; 413 pp.). The heads of hostages are chopped off and dumped in strategic locations around Singapore in this chilling adventure story pitting Muslim Fundamentalists against Western military technology. The hostages are passengers on a cruise liner that is captured by a deadly band of religious fanatics and blackhearted pirates. The beautiful heroine, Maggi Chancellor, is a professor and an expert on the local language and customs. As heads roll, one a day, a rather crazed Navy career officer sets out to rescue the hapless victims. Meanwhile, Singapore officials track down leads, torture suspects and unravel the motives behind the mayhem. A great deal of research went into this novel, on matters ranging from the habits of crocodiles to the firing of guided missiles. It's a first-rate thriller.