THE BERKUT By Joseph Heywood Random House. 490 pp. $18.95

Historian C. Vann Woodward drew a distinction in a recent essay between "historical fiction" and "fictional history." The former designation "is applied as a rule only to novels in which historical events figure prominently. Fictional history, on the other hand, portrays and focuses attention upon real historical figures and events, but with the license of the novelist to imagine and invent ... Of the two, it is fictional history that is the greater source of mischief, for it is here that fabrication and fact ... are most likely to be mixed and confused."

"The Berkut" is fictional history that contains its share of mischief. The central premise is that Adolf Hitler did not die in the bunker in Berlin in 1945 but instead escaped to the Harz Mountains in southeast Germany and from there was taken to an embarkation port in Italy with the connivance and active assistance of the Vatican.

The publisher has great expectations for this book. It is, as Random House claims, "a riveting thriller and a classic chase story" embellished with interludes of kinky sexual activity, bestialities and depravities of various description and slaughters on a scale appropriate to a novel that resurrects two of the most celebrated mass murderers in human history, Hitler and Stalin.

The novel is neatly organized. Its three sections -- "The Escape," "The Search," "The Pursuit" -- cover a period of exactly a year. A brief epilogue finishes the tale. The action is relentless. There is tension and suspense from beginning to end. It has all the trappings of a huge success.

But there is a problem here. "The Berkut" is not believable. Hitler is drawn as a petulant milquetoast who, eventually, finds solace in the arms of a young Jewish woman who has survived unspeakable atrocities at Buchenwald. His rescuers, splendid SS specimens and a killer pack of German girls called "Valkyries," are capable of martial and erotic feats far beyond poor Rambo's. His Soviet pursuers are formed from the same genetic material. Their strength, courage, brilliance, wisdom and capacities surpass all understanding. The malignancy of their master, Stalin, is on the same scale.

There is a lot of hyperbole and malarkey in most of our favorite thrillers; that's part of their attraction. But there are limits to what most of us can swallow. Joseph Heywood, in my view, has exceeded them.

He tells us in a postscript to the novel that there is substantial doubt about Hitler's demise and that, therefore, the large thrust of his story might well be true. Nahhh. It didn't happen that way, not even in the movie-to-be. The reviewer is deputy managing editor of The Washington Post