TOM CLANCY probably surprised no one more than himself by the runaway success of his first book, The Hunt for Red October. A fictional account of the defection of a Soviet submarine to the United States, it was extensively based on his hobby of wargaming and might have been expected to appeal not much further than the brotherhood of that strange enthusiasm. Unusually in a wargamer -- a type which often comes as close as any earth-dweller to embodying what Hollywood likes to call "alien life form" -- Clancy had the imagination to turn the game's convolutions into dramatic narrative. Red October sold 336,000 copies in hardback. The author deserved every cent in royalties that it made.

He has now cast the net of his imagination even wider. Red Storm Rising supposes that an oil crisis drives the Politburo to the supreme risk of venturing a conventional attack against NATO in Central Europe as the necessary preliminary to seizing the oilfields of the Persian Gulf. The Russians' strategic purpose is to cripple NATO's ability to interfere with their Middle East operation, but not so severely as to provoke the West into using nuclear weapons.

The war which he describes -- with uncanny realism -- unrolls in three dimensions, land, sea and air. At sea a great deal of the action turns on the form of operations in which he first demonstrated his extraordinary grasp of technicality: antisubmarine warfare. But his narrative of ship versus sub and sub versus sub tactics goes hand in hand with a dramatic depiction of carrier operations and of the fraught venture of running convoys through hostile waters.

His grasp of the complexities of modern air operations is equally acute. He maneuvers fighters against fighters, fighters against bombers, bombers against ground targets, missiles against all three and anything that will fly against electronic early warning aircraft with a sureness of three-dimensional touch that prompts the reader to wonder whether the Pentagon wouldn't be spending some of its millions better at employing him inside Cheyenne Mountain than letting his talents go to waste in mere best-selling authorship.

His land battle scenarios are set in widely separated and varied localities. The Soviet war plan requires that one of the Russian airborne divisions seize Iceland, as a flanking position from which to menace the reinforcement of Europe by transatlantic convoys. So Clancy has it landed by subterfuge with what proves to be outstanding success. The only effective survivors of its descent are a party of Marines and an Air Force officer who, between them, play a key role in keeping NATO intelligence informed of Soviet machinations.

Those bear directly on the fortunes of the NATO armies in Europe which, outnumbered as they would be in reality, can only hope to stem the tide of the Warsaw Pact onslaught with the help of major reinforcements from the United States and massive infusions of material from the same source. The author's depictions of tank battles and river crossings on what NATO calls the "Central Front" are particularly well done. Those who have read an earlier essay in the genre, General John Hackett's Third World War, which President Carter is said to have kept on his bedside table, will wonder why that effort won the plaudits it did. It bears the same resemblance to Tom Clancy's flights of imagination as a high school essay does to a PhD dissertation.

The author even manages to invest some of his characters -- who play an essentially subordinate role to the machinery -- with something like hot blood and real emotion. That is particularly so in the case of one Soviet commander who directs operations on the Central Front. It proves a successful device to tell the story of the Soviet attempt at breakthrough from the Russian rather than American point of vview. "Pasha," as he is nicknamed, is quite a convincing warrior figure, whose value system harks back to the ordeal of the "Great Patriotic War," as Soviet citizens are taught to call World War II, and who therefore harbors essentially moderate views about the efficacy of nuclear weapons. IF THE BOOK has a flaw, it is that it presupposes cooler thinking on both sides than we can hope would be the case if a conventional war did break out for real on the Central Front. Time and again the reader finds himself thinking, "Surely this development must prompt the opposition to escalate." Clancy brings NATO perilously close to defeat without even hinting that Washington, the NATO high command or what would surely have been some terrified NATO allies uttering as much as a bleat of demand for "nuclear release." In reality -- and if deterrence means anything -- nuclear requests and nuclear threats would have been uttered long before the pass to which Clancy brings NATO would have been reached.

These, however, are quibbles. There is now a long tradition of military futurology in Western literature, which includes such remarkable works as Jules Verne's Twenty Thousand Leagues Under the Sea and H.G. Wells' The War of the Worlds. Red Storm Rising will take its place with those two triumphs of bellicist admiration. It is a brilliant military fantasy -- and far too close to reality for comfort. John Keegan, author of "The Face of Battle" and "Six Armies in Normandy," is the defense correspondent of the Daily Telegraph of London.