"It is sometimes said that there are Reds under every bed. Perhaps this saying should be amended somewhat."

-Kremlin spokesman Gennadi Gerasimov, commenting on the spy- for-sex scandal that has resulted in the arrests of four U.S. marines.

IT IS THE STUFF of spy novels, diplomatic folklore and congressional investigations. A foreigner arrives in the Soviet Union. He is bored and lonely, deprived of the constant stimulations offered by life in the capitalist west. One day, he meets Tanya, apparently by accident. She is blond, buxom and high-spirited, a sparkling contrast with the dreary monotony of everyday Soviet life. They fall in love. By the time he discovers that she is a KGB plant, it is already too late.

The sex trap outlined above is so corny that it may be difficult to believe that it works in real life. But the historical record shows that it does -- over and over again. The latest espionage allegations against U.S. marine guards in Moscow and Leningrad are simply another reminder that, in an age when espionage is becoming increasingly technology-intensive, the oldest trick in the KGB manual is still one of the most effective.

The list of known KGB entrapment victims since World War II is long, distinguished and remarkably varied. It includes men and women, bachelors and married couples, young and old, homosexuals and heterosexuals, military attaches and journalists, security guards and ambassadors. No category of western resident in Moscow, it seems, has been immune from the charms of Soviet "swallows" and "ravens," KGB jargon for professional seductresses and their male counterparts.

"It's a very crude technique -- but one that the Soviets employ with considerable sophistication. You would have thought that we would be selecting people who were invulnerable to it by now, but apparently not," says John Barron, author of two standard works on the KGB. British journalist Phillip Knightley, author of "The Second Oldest Profession -- Spies and Spying in the Twentieth Century," explains: "Every westerner who goes to Moscow knows that some girl may get into his bedroom, but people continue to get trapped . . . . It's human nature, I suppose."

The exploits of the spy-seductress -- an occupation that could be said to combine the world's oldest and second-oldest professions -- are best described as tragi-comedy. There is something inherently risible about a starched-pants marine or a striped-pants diplomat losing his starched/striped pants while on active duty for his country. The suave Soviet Foreign Ministry spokesman, Gennadi Gerasimov, made light of the plight of Americans in Moscow when he poked fun at "28 strong marines" for "allegedly being unable to withstand the charms of blond spies." "Recently we have witnessed a loss of capabability to resist the enemy," he told an appreciative press conference.

For the individuals involved, however, there is also deep personal tragedy. In his book, "KGB -- The Secret Work of Soviet Secret Agents," Barron documents the case of a French military attache, Col. Louis Guibaud, who committed suicide in 1962 after an affair with a Soviet woman. Confronted with the evidence by the KGB, and offered the choice of secret collaboration or public disgrace, the colonel preferred to shoot himself. A similar dilemma confronted Jeremy Wolfenden, a British journalist in Moscow in the early 1960s, whose homosexuality made him a natural KGB target.

"In these situations, the way out is often fraught with danger," says Knightley, who has written about the Wolfenden case. "If you go back and tell your own side that you have been framed, they will frequently try to recruit you as a double agent. That's what happened to Wolfenden and eventually it drove him to suicide."

Sexpionage is always a long-odds gamble. Most westerners who have spent any length of time in Moscow have their favorite tale of an attempted seduction by a KGB swallow or raven. Most approaches fail. But, as the case of the U.S. marines has shown, it only takes several successes for the security damage to be considerable. "The machine cranks on and turns up enough gems for the expense of the operation to be worthwhile," says Donald Jameson, a retired CIA analyst. "The net is cast very wide. Of 100 prospects, less than half result in an incident. Perhaps 10 result in a compromise and only one results in an agent -- but that one agent is worth the effort."

Heading the list of entrapment victims are three former western ambassadors, men who had reached the pinnacle of their profession and were regarded as above reproach by their governments when assigned to Moscow. Prior to the marines, the most recent known attempt to compromise an American official involved a high-flying U.S. military attache on a visit to a provincial town. All four stories are interesting, and worth telling in some detail, because they illustrate four variations on a very basic technique. When John B. Watkins went to Moscow as Canadian ambassador in 1954, the Soviet Union was in the midst of a political thaw, similar in some ways to the "glasnost" period today. The dictatorial Joseph Stalin had just died -- and Nikita Khruschev was opening up the gulags. It was a fascinating time to be in Moscow -- and Watkins seemed the perfect ambassador. He was sophisticated, erudite and fluent in Russian. He had enormous curiosity about the vast country to which he was accredited -- which he satisfied by taking long trips into the provinces, frequently alone. He was also, it later turned out, a homosexual.

According to William Kaplan, a law professor at the University of Ottawa who is writing a book about Watkins, the ambassador met a Soviet man with whom he had a brief affair on one of his trips to Central Asia. The man later sent the ambassador a postcard, suggesting that they meet in Moscow. The encounter took place in a hotel room -- and their amorous embraces were secretly filmed by the KGB. It was not until Watkins was about to leave the Soviet Union in 1956 that he was confronted with the evidence of his brief affair by the KGB -- and an attempt was made to recruit him as a Soviet "agent of influence." As a top official in the Canadian foreign ministry, he would have been enormously valuable.

Kaplan, who has researched the case extensively and received his information from the Canadian security services, believes that Watkins never helped the Soviets significantly. There was, however, a tragic conclusion to the story. After the Canadian security services found out what had happened through a Soviet defector, it sent agents to question the former ambassador in retirement in Paris. He was brought back to Canada where he died on Oct. 12, 1964, of a heart attack in a Montreal hotel room while under interrogation by the Royal Canadian Mounted Police. Handsome and worldly, Maurice Dejean had served as a senior aide to Gen. Charles de Gaulle in the "Free French" movement in World War II. As France's ambassador to Moscow in the early 1950s, he was a tempting target for the KGB. Soviet agents in Paris were predicting that de Gaulle would soon return from the political wilderness to save the nation from the trauma of the war in Algeria and the instability of the Fourth Republic. It seemed likely that Dejean would end up in an extremely influential position in Paris. An operation of unprecedented magnitude -- involving more than 100 highly-trained agents -- was set in motion to entrap him.

According to one of the agents involved who later defected to the west, Yuri V. Krotkov, the KGB played on Dejean's vanity and his reputation as a womanizer. The ambassador was given what seemed like extraordinary access to influential Soviet officials and cultural figures -- nearly all of whom were cooperating with the KGB. He was also introduced, at carefully arranged "chance" meetings, to a bevy of attractive swallows. The sting closed around Dejean when an aggrieved "husband" (actually a KGB agent) discovered the ambassador in bed with his long-legged "wife," beat him up and threatened to create a big scandal.

The amorous Frenchman was offered a way out of his predicament by a senior Soviet government official (another agent) with whom he had earlier become friendly. The scandal could be hushed up -- but favors would be expected in return. As it turned out, Dejean was never activated as an agent. Krotkov's defection put an end to the operation -- and the ambassador was recalled. As described by Barron, the final humiliation came in a frosty interview with de Gaulle. Looking down from his great height, the general dismissed his errant protege with a single sentence: "Eh bien, Dejean, on couche." (So, Dejean, you've been sleeping around.) Tall, elegant and dignified, Sir Geoffrey Harrison looked and sounded like the epitome of the stiff-upper-lipped Englishman. By the time he was posted to Moscow as Her Britannic Majesty's ambassador in 1965, he had a well-deserved reputation as a particularly skillful diplomat. Happily married, with four children, he also seemed a particularly unlikely candidate for KGB entrapment techniques.

One day, Lady Harrison fell down on the highly-polished floor of the embassy ballroom -- just across the Moskva River from the golden domes of the Kremlin -- and broke her wrist. She was flown back to England for treatment. While she was away, Harrison had an affair with an embassy maid, Galina, who was described by a subsequent British ambassadress as a "blond of ample proportions" who "really looked a bit of a tart." "As a trained diplomat, it was an aberration on my part . . . absolutely crazy," Harrison told newspaper interviewers in 1981 after the story broke. "I did not ask whether she was working for the KGB, but the assumption was that every Russian working in our embassy was a KGB employe."

Harrison later confessed his "aberration" -- and the KGB never got a chance to use him as an agent of influence. He was recalled to London a few days after the Soviet invasion of Czechoslovakia in August 1968.

The sequel to the story took place in Buckingham Palace when the head of the British Foreign Office had to report the incident to Queen Elizabeth II. The coat-tailed diplomat feared an outburst of royal indignation at the indiscretion of a trusted ambassador. In the event, according to Foreign Office folklore, Her Majesty dissolved into royal giggles. Maj. James R. Holbrook was one of the most gifted linguists in the U.S. Army. Before being assigned to Moscow as assistant U.S. military attache in April 1979, he had served in the U.S. military mission in Berlin. He was tipped as a candidate for the post of military adviser to Vice President Bush, a position that would have given him access to high national secrets.

Like other western military attaches, Holbrook spent a lot of time on the road, engaged in a form of legal spying that is widely practised by both sides. In January 1981, he visited the Ukrainian city of Rovno with a fellow U.S. attache, Lt. Col. Thomas A. Spencer. Somehow, KGB agents succeeded in drugging the two attaches and separating them from one other. According to an official familiar with the details of the case, Spencer became unconscious while the KGB tried to get compromising photographs of Holbrook with a KGB swallow. A Soviet colonel known to Holbrook from his Berlin days then mysteriously appeared to offer his old friend "help". The two U.S. officers were immediately recalled to Washington after reporting the incident to their superiors, and according to the Army, both have since been promoted.

A common thread running through all these stories is that sexpionage has claimed some improbable victims. "We are not talking about 19-year-old high school graduates from Middle America like the marines. We are talking about very experienced people who should know better," says Kaplan, who will publish a book of correspondence by Watkins (entitled "Moscow Dispatches") this fall. Kaplan says that the former Canadian ambassador "knew very well that the secret police was out there -- but I don't think he really believed they would act in such a despicable manner."

"It's naive to think that, in a controlled and hostile environment, you can behave as you would in a place like England or France," remarks Barron, who has studied many KGB entrapment cases. "What people fail to recognize is that operations like these involve much more than simply a boy-girl relationship. It's not a situation in which the lone westerner is confronted by the lone Russian temptress. In reality, it's one isolated individual against a massive, very experienced apparatus. All the circumstances are controlled by the KGB to maneuver the victim to a desired end. Sexual enticement, and the lure of a fulfilling relationship, is just a first step across the threshold. But once it is taken, retreat can be very difficult."

John Vassall, a British navy clerk who was recruited to work for the KGB in the 1950s after falling victim to a homosexual trap, described his experience this way when released from prison in 1972: "It was like a spider's web. It was done very, very cleverly. At no time could I have escaped. I just got more and more entangled."

The evidence suggests that Soviet attempts to frame westerners living in Moscow are as likely to occur at times of political thaw and detente as during periods of cold war. Like other sectors of Soviet society, the KGB operates as if it had a "plan" to fulfill, preferably overfulfill. It sometimes seems as if the secret service apparatus is obliged to "produce" a certain number of victims, whether or not they can be put to any good use.

According to Kaplan, the challenge of dealing with the Russians during the earlier period of "glasnost" in the mid-1950s was one that fascinated Ambassador Watkins. In a dispatch to the Canadian foreign ministry, Watkins made the following comment: "It sometimes feels here now as if the Russians have just reread the old story of the contest between the wind and the sun to get the man to take his coat off -- and have decided for a change to turn on the full warmth of their renowned Slavic charm and see how it works. I don't see why we shouldn't take our coats off and be sociable, but we must be careful to resist any wild impulses to divest ourselves of more of our attire than would be prudent or seemly."

That dispatch was filed in 1955 -- at just about the time that Watkins was himself allegedly being seduced by a young Soviet "raven." Michael Dobbs in a Washington Post reporter.