I don't want to belittle Leonard Gross's contributions to ''The Dossier,'' but Mr. Salinger's are so obvious and so central to the novel's plot, characterization, and point of view that it is difficult to remember that Salinger did not write this book by himself. Salinger brings background and experience to ''The Dossier'' which give the book realism and believability and which make the main character's ethical dilemma understandable. That character, Andre Kohl, is a likable man obviously based on Salinger himself.
Both Kohl and Salinger are in their late 50s and both are the sons of Jewish fathers and French Catholic mothers. Both were piano prodigies, saw action in the Pacific as naval officers during World War II, and wrote books about John F. Kennedy. Both have had long, successful careers in journalism as writers and editors for magazines and newspapers and as Paris-based network news correspondents.
As the book opens, Andre Kohl has just begun a year's leave of absence from his job with the United States Broadcasting Corporation to explore ''the road not taken,'' the musical career he abandoned years ago in favor of journalism. His plans are abruptly changed when he receives a tip from an Israeli informer about the existence of a dossier that implicates French presidential candidate Camille Laurent, a staunch anticommunist whose election is almost certain, in collaboration with the Nazis during World War II.
In his quest for the dossier and the story of a lifetime, Kohl becomes an unwitting pawn of the KGB, which wants to prevent Laurent's election, and a target of both the French Secret Service and the CIA, which want to ensure it.
Throughout, Kohl wrestles with his personal and professional ethics. He knows the unwritten code of his profession dictates that a journalist report and interpret events but not perpetrate them. He also knows that if Laurent is guilty of collaboration, the information should be made public. If it is, Laurent will not be elected, but Kohl will have played into the hands of the KGB.
How Kohl finds the dossier, has it authenticated, and deals with his ethical dilemma - as well as with the KGB, the CIA, and Meredith Houghton - make ''The Dossier'' an exciting, intelligent novel. Its authors know their subject matter and how to present it.