THIS IS A DEEPLY disturbing book. It reads like a mystery novel, but sadly it's fact, not fiction, and it's not a who -done-it, but a why -done-it. It's the story of two young Californians, products of affluent families, with all their attendant (dis)advantages, who sold spy satellite secrets to the Russians.

The snowman is Daulton Lee, an adopted child, a runt of average ability who wanted to follow his physician father to Notre Dame. "Unfortunately for him," in the words of his psychiatrist, "his only average grades and below average stature frustrated these aspirations and left him with a deep sense of failure and a feeling of paternal rejection. This led to adolescent rebelliousness and acting out which entailed drug dealing." Did it ever entail drug dealing! Daulton soon progressed from smoking pot to selling it; then he went on to cocaine, or "snow," before graduating to heroin. It didn't take the Snowman long to establish a Mexican connection and a booming business among the idle young drifters of Palos Verdes.

Chris Boyce is taller and smarter than Daulton Lee. His father, a former FBI agent who enjoyed spending time with his young son, never seemed to notice that Chris was growing up with a number of ideas diametrically opposed to his own conservatism. For example, in his avid reading of history, Chris had concluded that nationalism was an evil force leading only to human suffering. Did not the reports from Vietnam daily confirm his conclusions?

By the time he finised high school, Chris seemed almost a burnt-out case. He had lost faith in his church and his country, his family and himself. The only thing which buoyed his spirits was his hobby -- catching and taming falcons. Hunting with these birds was the only thing that really mattered to Chris, but it couldn't support his growing drug habit, so after drifting out of one college and then another, he decided he needed a job.

His father was happy to use his connections to find him one at TRW, a manufacturer of high technology equipment such as satellites. After some perfunctory background checks, Chris was given a security clearance and put to work as a $140 per week file clerk. He was a conscientious worker, and he soon found himself promoted to work in a super-secret vault surrounded by documents of the utmost sensitivity, documents describing satellites with eyes a hundred times more sensitive than those of his precious falcons.

Had Chris entered a highlyl disciplined operation with the constant crosschecks and tight supervision one would expect in the inner sanctum of a hush-hush spy factory, I doubt that he ever would have seriously entertained the notion of smuggling anything out for the Russians or anyone else. But conditions inside the vault were unbelievably lax. As long as things seemed to be going smoothly, Chris' supervisors, who did not themselves possess the security clearances required to gain access to all the material in the vault, simply turned their backs on the entire operation. Only those with a "need to know" were cleared for entry into the vault. Even the guards outside the door were not allowed to enter -- all this in the name of security! But how were authorized couriers greeted? "Morning visitors to the vault could expect vodka and orange juice; afternoons, there was often peppermint schnapps, red wine, or daiquiris whipped up in the CIA's document-destruction blender."

The free and easy life inside this bunker became the main topic of conversation between the two childhood chums, the Falcon and the Snowman. The Snowman saw Easy Street just around the corner, if only he could get enough cash to make a really big buy in Mexico. The Falcon saw how simple it would be, and besides, he didn't like the CIA one damn bit. Those cruds were always trying to wrap their rotten schemes in the false flag of patriotism, and it was time to put a stop to it.

So the deal was consummated, and the smuggling of documents to the Russian embassy in Mexico City began. This is the most frustrating part of the book, in that Robert Lindsey is not able to explain with any precision exactly what triggered the momentous decision. However, after listening to what the two had to say after being caught, one concludes that they themselves really didn't know. Daulton's drug-crazed greed is fairly easy to understand. After their arrest, Chris described Daulton as a "hoodlum." When pressed, he opined that he himself was an "adventurer," but that word falls far short of summarizing his confused and convoluted thought process. He certainly was not a Communist. It's just that somehow, in rejecting the simplistic credo of "my country, right or wrong," he seems to have justified to himself the substitution of "my country's enemies, right or wrong."

Who could help us understand what prompted these children to transit so casually from adolescent rebellion to betrayal of country? What insights did the Lees and the Boyces have? "It seemed strange to us that he Daulon never worked but seemed to have money," said the Lees. Chris' parents maintained that "although Chris had smoked marijuana once in high school, . . . it had made him sick, and he didn't have a drug habit." Frightening, that the adults who should have known them best knew them not at all.

This book abounds with frightening notions. For instance, how easy it is to spy! It takes no training, no special aptitude -- just access to sensitive information and a willingness to sell it. If two bumbling amateurs could be this successful, consider what a pro, or a shrewd amateur might have done, or might be doing today. Consider also the fact that these two chowder-heads nearly got away with it. Even after they were finally caught, the government almost decided not to prosecute, because the CIA feared the release of sensitive documents during their trial.

Or consider Daulton Lee, who had been arrested seven times in six years on various drug and traffic charges, and whose lawyer was a master at keeping him out of jail by exploiting constitutional safeguards and sympathetic judges. It's not hard to understand then why Daulton felt he could beat any rap, and this contemptuous attitude played no small part in his decision to become a spy.

The Falcon and the Snowman is Lindsey's first, and one hopes not his last, book. He is a thorough researcher and a straightforward storyteller, generally hewing to the main line. He can't resist an occasional aside, however, and some of them are downright silly, such as: "By the early 1970s, no KGB agent had ever penetrated the U.S. Satellite operations." Sez who, the CIA or the KGB? The former wouldn't know, and the latter wouldn't tell. But I don't mean to nitpick, Lindsey has told this sad story adeptly, unraveling a complicated sequence of events with clarity and sensitivity. But still, the basic mystery remains: why "two, young men who had begun life with what seemed to be the best that America could bestow on its children" decided to pay America back with treachery.