THE MOST STRIKING common denominator of the victims of Charles Sobhraj, the half-Vietnamese, half-Indian drugger, robber and murderer, is their gullibility.

Somehow during the early and mid 1970s the age-old admonition to beware of the dark handsome stranger seems to have been forgotten by the mostly young and footloose wanderers who drifted through the Far East. Because of their gullibility, or perhaps because of their implicit but misplaced trust in anyone with long hair, scores and scores of them lost their money, their credit cards and their passports, and at least a dozen lost their lives, murdered by a man who changed indentities as often as others change their socks.

These two books about Charles Sobhraj tell essentially the same story. The Thompson book is hardcover. The Richard Neville-Julie Clarke is an original paperback. The Neville-Clarke book has pictures. The Thompson book doesn't. Thompson's style borders on the lurid, for which he may be forgiven because he had to deal with a definitely lurid subject. The Neville-Clarke style is a bit quieter, almost stolid. Both books are eminently satisfying if your taste runs to the works and deeds of perfectly wicked villains.

For Charles Sobhraj is a proper villain, no doubt about that. Besides being a mugger and a killer, he was also a con man, burglar, escape artist, thief, smuggler and consummate liar. He spoke six or seven languages, perhaps more, neither drank or smoked, and shunned any drugs stronger than aspirin. And he had, of course, a perfectly rotten childhood.

Born the illegitimate son of a Vietnamese mother and an Indian father in Saigon during the Japanese occupation, Sobhraj was in trouble with the authorities early and often. His mother married a French army lieutenant and went to France with him, leaving her son behind with his real father who despised him. His stepfather refused to adopt him or give him his name and Sobhraj, from the beginning, was a stateless person without identity. Later he would compensate for that. Overcompensate, in fact.

Finally, after the fall of Dienbienphu, he was reunited with his mother and his French stepfather in Marseilles. By now he was a chronic bedwetter and troublemaker. And by 1964 he was also an accomplished thief for which he was sentenced to three years in Poissy prison.

It was after getting out of prison that Sobhraj's real criminal career began. It was a career of preying on tourists, on the innocents abroad, who fell under the spell of the mysterious, well-spoken stranger who inevitably knew the best places to shop and dine and party. Should the tourist be looking for girls or boys or drugs, Sobhraj was most accommodating. Sometimes during the frolicking he would slip a drug into their drinks, help them to their rooms and strip them of their passports and valuables. Sometimes, as a final touch of panache, he would saunter up to the hotel's front desk, present his latest victim's room key and demand the contents of the locked box or safe.

Over the years, Sobhraj operated in Switzerland, Yugoslavia, Greece, Turkey (the Hilton in Istanbul was a favorite of his), Iran, Afghanistan, Pakistan, India, Nepal, Singapore, Thailand and Hong Kong. He would drive a stolen car from Zurich to Delhi as casually as someone else might drive from Dallas to Washington. Once he was jailed in a Greek maximum security prison, but managed to escape. Later, he would do the same in India.

But it was not until he reached Bangkok that Sobhraj began to murder for money. By now he had acquired a French-Canadian mistress and they operated out of a Bangkok apartment, where Sobhraj had set himself up as a gem dealer. But Sobhraj's method remained essentially the same. He would befriend his intended victim, drug him -- or her -- and steal their valuables. Only now he also killed them.

In their book, Neville and Clarke actually get Sobhraj to confess to the Thailand murders. But he claims that a mysterious Hong Kong heroin king paid him $500,000 to do the killings because the victims were all rivals in the international drug trade. Sobhraj is a marvelous liar.

Both Thompson and Neville-Clarke give portraits of Sobhraj's victims, and it is here that the two books diverge most widely, although there are many other nagging discrepancies. One young female victim of Sobhraj's is described by Thompson as a gifted, intelligent young California woman suffering from a tragic marriage. Neville and Clarke portray her as a dope fiend with a hopeless habit.

Finally, in Delhi, Charles Sobhraj and his French-Canadian mistress were arrested for the murder of a French tourist and brought to trial. The Thompson book tells how the trial came out; the Neville-Clarke book doesn't.

While reading both books, I kept seeing a recurring image.It was of the two young American tourists in the television commercial running into the European hotel and screaming about how they've just lost all their traveler's checks. Never again will I be able to view that commercial without thinking of Charles Sobhraj who, Thomas Thompson warns us, believes that "the serpentine roads of destiny" will eventually lead him to the United States.

Look out.