"Dear President Reagan," Mrs. Clifford N. Bevens wrote shortly before her husband's death, "As president of the greatest nation in the world, can you secure Cliff Bevens' freedom?"

President Reagan could not, Clifford N. Bevens, 56, president of a Goodyear International subsidiary, was kidnapped from his Guatemala City apartment Dec. 7. For more than seven months nothing was heard from him. On Aug. 13 Guatemalan security forces burst into a suspected guerrilla hideout, apparently oblivious to Bevens' presence there, and Bevens died along with five guerrillas of the rebel armed forces.

The complex game of abduction, ransom and death that constantly threatens businessmen, politicians and anyone with money or power in this part of the world is no more responsive to the U.S. government than to the pitful pleas of the victims' families.

Extortion is a cruelly refined art that few people understand, and as the kidnap industry has grown to phenomenal proportions in this part of the world, even the gangs themselves often seem to have little idea of what they are doing.

Somebody here in San Salvador made a big mistake last May, for example, when Teofilo Siman was snatched in front of his house.

In El Salvador the vast majority of kidnapings for ransom have been carried out by guerrillas buidling up their war chests. In recent years they have extorted, by most estimates, $150 million. So the minute it was known that Siman, whose family owns a large department store, was being held, it was assured that the left had done it once again.

But Siman, 55, is not just a businessman. He is the vice president of the Salvadoran Red Cross. He has no known political connections, and among his various charitable works he is the patron of an orphanage.

In the aftermath of his May 8 abduction, the Salvadoran press was full of emotional allusions to his good works, including photographs of the orphans praying for his release.

For the first time in memory, the guerrillas denied that they snatched someone. On May 18, the guerrilla Radio Venceremos said none of the factions under the joint command of the Farabundo Marti Forces of National Liberation had anything to do with the abduction.

Aware of their international image, the guerrillas said "any accusation blaming us for this incident is aimed at discrediting our forces."

Then, attempting to turn the tables, the broadcast warned that "the 'government' security organizations are holding stationery with our letterhead on it," although no reporting on the case ever mentioned guerrilla stationery.

On May 16, 1980, according to the broadcast, the police raided the home of Francisco Jose de Paz. "Inside Paz's house we had letterhead paper and the complete documentation of notes and communiques on the kidnapping of Adol,fo McEntee. We also had $1 million in that house. Part of this money, $600,000, was the war tax the McEntee family had paid." Paz, his wife and maid were murdered that night, the broadcast said. The documents and money were never accounted for.

The guerrillas concluded that in all their kidnappings and other actions, "We had acted in accordance with the rules and principles that we maintain as revolutionaries."

The Siman family and the police would not comment on the case. Families rarely do, even after the return or death of the victim because many groups of kidnapers keep up various kinds of threats long after the business is over.

From interviews with security experts and other sources, however, it is possible to piece together a fairly detailed picture of just how most kidnap operations are carried out and how the rich try to protect themselves.

In Guatemala, El Salvador and Colombia -- the three countries in the area where guerrillas, abductions and assassinations are most common -- personal security is an obsession among the rich and the political.

Those who stay in the country often live surrounded by high walls complete with multiple television surveillance cameras. Guard dogs and heavily armed bodyguards roam the grounds and bullet-proofed Jeep Cherokee Wagoneers costing more than $70,000 have become the accepted mode of transportation.

Ideally, according to American security experts, there should be two of these cars, one for you, the other filled with some of the six or seven gunmen necessary for "adequate" protection. These men should carry high quality arms, which means a minimum of $500 apiece, and their salaries should be high enough, at least $250 a month, to keep them faithful. All of this costs, after the initial investments, at least $60,000 a year.

Many of the rich carry their own guns, although how effective they are is open to question.

Another option for potential victims is to become as anonymous as possible, driving Volkswagens or even less well defended means of transportation.

One prominent right-wing leader in San Salvador rides a motorcycle. "I just had to make the decision how I wanted to live. And I did not want to live surrounded by guards all the time," he says.

A key problem is lifestyle. As one American put it, "You can't run down to the No-Tell Motel with your little honey for a nooner with all those folks around."

"With Salvadorans," said one security official here, "class patterns still exist. They won't listen to their bodyguards' advice because they consider them beneath them. It's symptomatic of the whole sickness of this society."

So they keep getting snatched.

The minute the kidnapping takes place, an elaborate, very personal kind of psychological warfare begins.

"The best tactics for the kidnapers are the simple ones," said one personal security advisor, "and they rely upon fear."

Sometimes the first ransom note is delivered immediately, before the relatives of the victim can be put under surveillance by the police. Other gangs wait awhile, often about three weeks, so that the family's fears will build and their resistance soften to whatever demands are made.

The victim will have been dragged from one car to another usually within the first 30 minutes, then put in what may be the first of several safe houses. In some cases the victim is treated fairly well. Leftist kidnappers in Colombia last year, for instance, abducted a 12-year-old girl and held her on a farm in a remote section of the countryside. After her family paid a ransom of about $3 million, she was returned. A few days later a duck she had made her pet on the farm was delivered to her house, according to one source close to the family.

But the captivity can also be extremely rough. A Salvadoran criminal gang operating in Guatemala this year delivered the finger of one of its victims to the family. It was hidden in a submarine sandwich. Another gang sent several of a young woman's teeth to her family in order to push them along.

According to friends of the Siman family, for the 37 days that Roberto was held last year he spent most of his time chained to a bed with wax pressed into his ears and a hood over his head.

"The victims normally come away sadder but wiser," said one security expert. "It's normally given them a lot of time to think about their values. It's a time of intense personal reflection. You're the man on the gallows."

In many cases the families become obsessed with the identity of the kidnappers, but even after the release of the victim that is often difficult or impossible to determine unless the gang openly claims responsibility.

In Guatemala, for instance, both the extreme left and the extreme right are believed to use kidnaping as a fund-raising tool.

Attempts are sometimes made by the right to blame a kidnapping on the left, or vice versa, as may be the case with the Siman kidnapping. Then there are criminal gangs masquerading behind political fronts and political groups pretending to be common criminals.

But in general terms, said one private security expert, "the leftists often identify themselves. The right ususally profess to be criminals."

In both Guatemala and El Salvador, said the expert, "the leftists are happy to claim openly what they have done, except perhaps in some cases such as Siman's. They sign their notes with a rhetoric that seems almost an attempt to justify doing it." They talk of war taxes and lofty revolutionary principles. "It's sad in a way."