IN FIGHTING a spy war against the Soviet intelligence machine, defectors are indispensable. They expose Moscow's espionage network. They reveal what the Kremlin is particularly interested in. They help the West to develop defenses against Soviet penetration and disinformation.

Yet, sometimes defectors do more harm than good. Some only pretend to change sides and continue to operate under Moscow's control. A number eventually return to the Soviet Union. And it is rarely clear whether they became disillusioned with the United States or were phony defectors to start with.

Consider the case of KGB Colonel Vitaly Yurchenko. Upon his defection he provided some genuinely valuable information to the CIA. But then he suddenly appeared at a Soviet embassy press conference in Washington claiming to be a victim of CIA kidnapping. One school of thought argues that the CIA mishandled the man to the point that under heavy emotional stress he opted to take a chance with his former masters. Others suspect that Yurchenko was a Soviet plant sent to embarrass the CIA and to discredit true defectors. The dispute may never be resolved.

But a defector does not have to be a double agent to do a lot of damage. Quite a few of them are emotionally unstable and even outright paranoiac. Many tend to exaggerate their importance and knowledge.

KGB major Anatoly Golytsin, who defected in 1962, is a perfect example. There is no controversy over his bona fides. Some of his revelations were extremely important and were corroborated by a variety of sources. Still, gradually he evolved into somewhat of a menace. That was because, contrary to an abundance of evidence, he confidently argued that splits between the Soviet Union, on the one hand, and Yugoslavia and China, on the other, were just disinformation ploys. Nor was Golytsin successful in discrediting Andrei Sakharov, whom he accused of operating under the KGB's control.

His allegations that the KGB managed to position "moles" in the heart of U.S., British and French intelligence services were much more difficult to refute. Supported by then CIA counterintelligence chief James Angleton, Golytsin triggered a great deal of suspicion inside Western spy agencies. In a climate of mutual recriminations, many crucial intelligence and counterintelligence operations came to a virtual halt. Some CIA officials feel that Golytsin could not do better for the KGB if he was a plant.

VICTOR SUVOROV'S new book, Inside the Aquarium: The Making of a Top Soviet Spy, is another reminder of how unreliable defectors may be. The author, a former officer of the Soviet General Staff Main Intelligence Director (GRU), writing under a pen name, provides a long list of horrors that would make envious creators of such adventure tales as Rambo and The Red Dawn -- except that his account is supposedly a memoir of a highly placed Soviet espionage professional.

Horrors start right on the first page. As part of his initiation procedure, Suvorov is shown a film where a GRU colonel is being burned alive in a crematorium for his alleged treason. According to Suvorov, the GRU is so secret an organization that the mere mention of its name by an outsider would likely result in an arrest, interrogation and torture. Later, there is an account of students at the GRU academy getting an assignment to recruit innocent Moscovites to spy for the West. Upon successful completion of the project, the victims of entrapment would be sentenced for treason.

The reader also learns that Soviet special forces training for operations behind enemy lines includes real-life combat with so-called "puppets." As Suvorov explains it, " 'a puppet' is actually a man -- a special kind of man for training purposes. For example, you can hit him, but unlike your partner in a match or your instructor, a 'puppet' is a criminal who has been condemned to death." The rationale is to postpone his punishment in order to allow special forces troopers to upgrade their killer techniques.

Actually, according to Suvorov, GRU staffers are not treated much better than condemned criminals. While stationed with the Soviet GRU office in Vienna, Suvorov was ordered to drop a Bible in a fellow officer's mailbox. This was done in order to see if the GRU man would immediately report the incident to his superiors. He failed to do so and was sent back to Moscow, where he had to face a long prison term.

Seniority does not protect against swift arrest for the slightest indiscretion. Suvorov's superior, a colonel who served as a deputy chief in the GRU Vienna office, was seen with an unidentified woman. The colonel was summoned to the commanding general's office, where he was handcuffed by Suvorov. Then, as Suvorov tells it, he "dipped a white napkin in gin from a green bottle and swabbed the place where the needle was to enter . . . and inserted the needle carefully beneath the skin." After that the general himself took over the interrogation with an imminent evacuation to Moscow and likely execution to follow.

SOUND LIKE a second-rate spy thriller? It is. In conversation with me, several defectors from Soviet intelligence scoffed at the story of a GRU colonel burned alive. References to the GRU, contrary to Suvorov's tale, may be easily found in the Soviet open literature. Three Moscow lawyers, now American citizens, stated with full confidence that there was no way for dozens of Moscovites to be tried every year on phony treason charges without some gossip among the Soviet capital's legal community. There was none.

Similarly, the lawyers expressed total disbelief that condemned criminals were routinely used as "puppets" for special forces training. Such a thing would have become known quickly. Yet they have never heard of anything of the sort.

Soviet diplomats and intelligence operatives abroad frequently engage in all kinds of officially forbidden behavior. They regularly obtain and smuggle into the Soviet Union not just Bibles, but also dissident writings, including those by Aleksandr Solzhenitsyn, published in the West. Extramarital affairs are certainly not recommended, but they are often tacitly accepted as a fact of life. Just read Arakady Shevchenko's Breaking with Moscow.

Inside the Aquarium is the functional equivalent of a consumer fraud. It is built up as a memoir, but is actually a rather poorly written fiction. False advertising starts right on the cover. The book's subtitle is The Making of a Top Soviet Spy. Yet those who go through the pain of reading it discover that Suvorov was a junior agent with very limited access to anything of importance.

Inside the Aquarium is the fourth book by Suvorov for Macmillan. His first, The Liberators, was a straightforward, if not always reliable, story of a young officer's participation in the invasion of Czechoslovakia. But then Suvorov went on to publish three increasingly questionable volumes about the Soviet army and about Soviet military intelligence. His effort to offer a broad picture beyond his personal experience led to quite a few serious and easily documented distortions. For instance, Suvorov claimed that former GRU chief Ivan A. Serov "was dismissed and quietly liquidated" in 1962 (Inside Soviet Military Intelligence, p. 181). It so happens that I worked together with General Serov's daughter, Valentina, in 1967-1972. The general was very much alive.

After reading four books by Suvorov, I am confused about his illustrious career in the Soviet Union. In The Liberators he said that he served in one military district and in Inside the Aquarium in another. In his introduction to Inside the Soviet Army, General Sir John Hackett, who said that he knew Suvorov "personally rather well," stated that the author "went through the Frunze Military Academy" (Inside the Soviet Army, p. viii). But in Inside the Aquarium Suvorov himself talks solely about studying at the Military-Diplomatic Academy under the auspices of the GRU.

If Suvorov's books were based on fact, there would be no reason for him to continue using a pen name. A wealth of personal data provided on their pages would inevitably identify him to Soviet intelligence. Yet, we are told, his real name is kept secret for fear of Soviet retaliation.

There is no merit whatsoever in Inside the Aquarium. Presumably Suvorov assumed that Western fascination with espionage would assure a market for just about any book on the subject. The reading public does not deserve such contempt.