THE NEW KGB: Engine of Soviet Power. By William R. Corson and Robert T. Crowley Morrow. 560 pp. $19.95.

VIGNETTE NO. 1: On a recent trip to the Soviet Union, I dined with Victor Louis, the most famous reputed agent of the KGB in the world. Louis, who says he is a journalist, is an engaging and articulate man, Westernized in manner, and he spent the time at dinner in spirited defense of the Soviet system. At the end of the evening, he climbed into a gleaming silver Bentley amd drove off into the night.

Vignette No. 2: A few years ago, I dropped off my car (not a Bentley, not gleaming) to be serviced at a garage in my neighborhood. Another customer, a tall, white-haired and extremely courtly gentleman, realizing I was without wheels, offered me a ride home, and I accepted. It was only later that I relized my benefactor was Robert T. Crowley, who had been the assistant deputy director for operations of the Central Intelligence Agency, and as such the number-two clandestine agent of the CIA.

Crowley, now retired, and William R. Corson, another former intelligence man, have written a detailed and revealing book about the KGB. I doubt that Crowley and Victor Louis (whose real name according to The New KGB is Vitali Levin) have met, but if they could, it would make for a fascinating evening. They would go at it like two old sparring partners. The relative merits of the CIA and the KGB, and the two contrasting systems that bred them, would be discussed with considerable wit and erudition. At the end of the evening, neither man would have changed the other's mind. But the conversation would have been right interesting.

Intelligence agents live in a world that is rather different from that in which the rest of us reside, and they tend to think differently, too. Nothing is what it seems.

As only one example of the complexities of this subterranean world, Corson and Crowley recount the strange case of Yuri Loginov, who was arrested in South Africa in 1967 as a Soviet "illegal," that is, a spy without official (usually diplomatic) cover. The authors find his arrest by the "relatively inexperienced South Africans" to be odd, since illegals are the slipperiest of intelligence eels and the hardest to catch.

So the implication, although the authors do not say so directly, is that Loginov was a "dispatched agent," a KGB officer sent out, in this instance, in order to be caught. But for what purpose?

The authors cite a report that Loginov supported the story of another defector, Yuri Nosenko, who had turned up in Geneva three years earlier. Nosenko discounted the allegations of a previous KGB defector, Anatoli Golitsin, who had warned the CIA that it harbored a high-level mole. The argument over Nosenko's bona fides tore the CIA apart, leading to resignations, creating bitter enemies within the agency, and pleasing the KGB no end. Loginov, the authors suggest, contributed to the confusion at the highest levels in Langley: "In the view of some experts, his 'failed' mission was in fact a dramatic success."

AND YET the CIA, the reader should keep in mind, has permitted only what it wants to be published about the KGB to appear in the book. As a former CIA officer, Crowley was obligated to submit the book to the agency for clearance. The CIA says he did so. It also says that Corson did not submit the book and was not so obligated.

The New KGB is mistitled, since the bulk of this study deals, not with the modern KGB, but with the history of the "organs" of Soviet state security. One must plough through pages of detailed examination of the evolution of the Cheka, the OGPU, the NKVD, the MVD and so on, as well as descriptions of ancient shenanigans by Amtorg and other commercial arms of the Soviet government, to find the nuggets -- but they are there to be mined if the reader is patient enough.

For example, Corson and Crowley relate that Yuri Andropov, the first head of the KGB to become leader of the Soviet Union, and his prot,eg,e, Viktor Chebrikov, the present head of the KGB, met years ago on a dull, bureaucratic assignment, a KGB promotion panel on which the two men served for only two weeks. But they stayed in touch. In 1955, when Andropov was KGB resident in Hungary and later ambassador, he sent for Chebrikov as his deputy. The two won their spurs the following year when Soviet tanks and troops crushed the revolt in Budapest. When Andropov succeeded to power after Leonid Brezhnev's death in November 1982, one of his first acts was to appoint Viktor Chebrikov head of the KGB.

There is tradecraft galore here, descriptions of how the KGB goes about compiling lists of infant deaths, finding defunct businesses, schools and addresses to build uncheckable legends for its illegals. There is an account of the spy school at Bykovo, near Moscow, sometimes known as "Little Chicago," where Soviet agents were allegedly taught to pass for Americans. They were required to memorize batting averages, and taught by a faculty that "understood the importance (for legend purposes) of baseball, radio, hot dogs, and apple pie." Bykovo, according to the authors, even had a roller skating rink.

The New KGB spends a great deal of time telling us that the Soviet secret police killed 40 million people, that Stalin and Beria were responsible for mass terror, and that the KGB is not the Rotary Club. But the denunciations of the Soviet system, which permeate the book, are standard fare, hardly necessary to establish the authors' anticommunist credentials, and tend to detract from the narrative.

Despite the condemnatory tone, the authors, as professionals, cannot conceal their admiration for one Hans Galleni, a Soviet agent who showed astonishing ingenuity in outwitting the British secret service and tracking down "Scott," a cipher clerk in the British Foreign Office. The case is a tale well told.

And Corson and Crowley give a balanced appraisal of Andropov as KGB chief, concluding that he was a man of considerable skills as an administrator. Andropov chose his young officers with care: "The group cannot be seen as resembling political hacks or 'ticket punchers' of the sort seen in the past. Rather, they are the 'best and the toughest' the Soviet system has been able to produce in nearly seven decades."

On the other hand, the authors seem to accept the theory that Mehmet Ali Agca tried to assassinate the pope on behalf of the Bulgarian secret service, i.e., the KGB. Since books have a long lead time, of necessity they reached this conclusion before Agca, the star witness for the prosecution, unveiled the second coming in a Rome courtroom and disclosed that he was Jesus Christ.

There is a tendency for authors to become so absorbed in their subject that they may exaggerate its importance. Corson and Crowley have not escaped this trap. Thus we are told that the Soviet secret police have achieved the "dominant role in the Soviet government." And that "The KGB now operates the USSR, and Chebrikov heads the KGB." The logical conclusion would seem to be that the party and the military are subservient to the men from Lubianka, and that Viktor Chebrikov runs the Soviet Union. All of which would, to all outward appearances, be news to Mikhail Gorbachev.