(FORTUNE Magazine) – Midsummer is here, and so too -- with the precision timing of one of those high-tech weapons systems he describes in such exhaustive detail -- is the latest novel by Tom Clancy. In a 1986 FORTUNE survey, the favorite escape novel among CEOs was Clancy's first book, The Hunt for Red October. By now Clancy thrillers have evolved into something of a summer ritual, each hitting the bookstores just in time to be snatched up and tossed in the beach bag along with the huarache sandals and the aloe vera. The Cardinal of the Kremlin (G.P. Putnam's Sons, $19.95) continues the tradition, a perfect accompaniment to the music of the sand and surf. Clancy connoisseurs won't be misled by the title of this latest addition to the corpus -- they've met the Kremlin's Cardinal before. ''Cardinal'' is the code name of Colonel Mikhail Filitov, a CIA mole placed high -- very high -- in the Soviet military. In The Hunt for Red October, Colonel Filitov's data enabled the CIA to capture the most technologically advanced submarine in the Soviet fleet without letting the Russians know it had fallen into American hands. Now, on what turns out to be his final mission, he is asked to perform similar -- and similarly improbable -- intelligence wizardry in the superpowers' race to develop a strategic defense system, a.k.a. Star Wars. Besides Filitov, Clancy calls several other Red October characters into active service for The Cardinal of the Kremlin. Featured most prominently is his recurring hero, Jack Ryan, a CIA deskman who can't seem to stay clear of the operational end when intelligence battles heat up. This time Ryan is the CIA's observer at arms-control negotiations. The proposal on the table -- calling for 50% reductions in each side's nuclear arsenal -- is blocked by an American refusal to forgo research and development (and eventually deployment) of a laser-based strategic defense. The Soviets, meanwhile, are rushing forward with their own Star Wars system at a station near the Afghan border even as they try to cajole the U.S. into giving up SDI. Sounds familiar? It's supposed to, of course. Clancy's method as a storyteller is to take today's newspapers (along with, he admits, every other unclassified document he can get his hands on) and weave a sort of alternative universe, using his novels to play an elaborate game of ''What if?'' Verisimilitude is the key. His descriptions of military hardware are the most complete to be found outside the offices of defense intelligence; real-life characters and events often appear in thin disguise. Fact blends with fiction to give the story its edge. In Cardinal, for example, the Soviet General Secretary -- called Narmonov here -- is a relatively benign reformer whose plan for liberalization is threatened from all sides by an entrenched elite terrified of losing its privileges. All Clancy's Gorbachev lacks is the birthmark (and the pushy wife). The hypothetical premise of The Cardinal of the Kremlin -- the ''what if'' -- revolves around the Cardinal himself. Having channeled secrets to the CIA for 30 years, Filitov is getting old, and his numberless betrayals of the state are taking their tolls. At night he sits alone in his Moscow apartment with a bottle of vodka and the memories of former comrades and of his wife and children, whose deaths he blames on the heartlessness of the state and avenges with treason. WHEN THE CIA and Ryan get wind of the Soviet SDI base near the Afghan border, they call on the Cardinal to secure a description of the base and the laser technology employed there. The Cardinal sends a subordinate, who returns with a detailed report that Filitov, through an elaborate line of CIA operatives, passes to the U.S. From this Ryan learns that the Soviets, while behind in the software necessary to construct a laser-based strategic defense, have nevertheless achieved a breakthrough in laser technology that has eluded the Americans. Although the CIA has reason to believe that the Cardinal is at last suspected by the KGB, it asks him to perform one last mission before it brings him ''in from the cold'': Find out how the Soviets have achieved their laser breakthrough, the missing piece in America's attempt to assemble the puzzle of SDI. At the top-secret Star Wars base in New Mexico, meanwhile, the Soviets have established a line of their own. Their operatives reveal the advances in SDI software that threaten to give the U.S. the world's most comprehensive strategic defense -- a prelude, the Soviets reckon, to war. Something close to panic sets in, although Clancy's characters are too professional to panic as you or I would panic, and intelligence leads to counterintelligence, which leads to a fair amount of low-tech bloodshed. Before long the KGB discovers the Cardinal and another CIA mole. Their arrests are kept secret from the Politburo by the hard-line, anti- perestroika director of the KGB, who plots to use them as tools to topple the General Secretary. With this, Ryan sees that the stakes have been raised: Not only is the Cardinal's life at risk, but also the future of strategic defense, and beyond that the future of Narmonov's move to liberalize the U.S.S.R., the success or failure of which will determine relations between the superpowers for decades to come. The CIA, with the aid of a homosexual Congressman, no less, hatches a complex (and sometimes confusing) plan, and once again Ryan the deskman becomes Ryan the operative. OH YES, one more thing. While the Soviets are trying to figure out what the Americans know, and the Americans try to figure out what the Soviets know, the reader knows what none of them know: Out in the Central Asian outback, a crack ! band of Afghan rebels are making their way across the rugged hills to the Soviet SDI station, bent on destruction. The U.S.'s attempts to keep a Soviet leader in power against the machinations of the Kremlin old guard create an unexpectedly ironic climax to the story, although the reader has much else to keep him interested along the way. The countless subplots interweave ever more tightly as the central plot progresses. On cross-examination, however, any honest Clancy fan will tell you that the chief pleasure of his books derives not so much from their brisk pacing as from the prodigious research and painstaking technical detail that undergirds them. In The Cardinal of the Kremlin one gets the feeling that this is how it would really happen -- that Clancy knows what techniques spies employ to pass state secrets, for example, or that he knows what the conversation sounds like when the director of Central Intelligence briefs the President. The Cardinal of the Kremlin sweeps along from a mujahedeen base camp to a meeting of the Politburo, from a Soviet reconnaissance plane to an American nuclear sub, and Clancy never breaks a sweat. IN Cardinal, plot and subject matter are more important than character, a cart-before-the-horse priority that separates pulp fiction from its loftier cousin, the Serious Novel. But this will strike Clancy fans as a lit crit cavil, irrelevant to the pleasures his books promise and invariably deliver. Cardinal and Clancy's other novels are themselves separated from the mass of pulp fiction by their extraordinary ambition: He aims not only to entertain but also to let his readers in on the ''inside story,'' meanwhile discussing with relish the strategic and technological issues of war and peace.

The Cardinal of the Kremlin can even be read (and will probably be criticized) as an extended brief in support of both the feasibility and necessity of the Strategic Defense Initiative. As a publicist he may betray the fictioneer's art. Politics in a novel, said Flaubert, is as appropriate as a gunshot in a theater. But Clancy's books perform a considerable public service nonetheless. Few subjects of American political discourse are as clouded with emotion and sanctimony as defense policy, and it is refreshing to find a member of the literati who is willing to deal with the topic in a manner more sophisticated than signing the latest disarmament petition in the New York Times. Through seriousness of purpose and much study, Clancy tries to understand nuclear weapons: their technology, their horror, and (alas) their inevitability. This is no small achievement. Let's hope Tom Clancy continues his summer tradition.

BOX: EXCERPT: The KGB Chairman opened ((the envelope)) and took out the photographs. He didn't display any reaction as he flipped through the three frames, but when he turned to look at Ryan his eyes made the morning's wind seem like the breath of spring. ''One's alive,'' Jack reported . . .

'' I should kill you here and now!'' Golovko said. They were in the Chairman's car. Ryan found himself facing four very irate KGB officers.