Boys and Their Toys : DARK GENIUS: The True Story of a Child Prodigy in the Shadow of the CIA, <i> By Kevin McClung and Stephen J. Rivele (Knightsbridge: $22.95; 484 pp.) </i>

While other boys were tinkering with their Tonka trucks, 6-year-old Kevin McClung was redesigning a toy rifle so that it would emit a 50,000-volt bolt of lightning. The invention was one of McClung’s few failures, but it set him on the road to a CIA nether world from which he says he is only now, at age 33, recovering.

McClung’s desire to take gadgets apart and then amplify their power was encouraged by the innovative Mentally Gifted Minor (MGM) program of his Bay Area school, which gave him the resources to build dozens of projects for individual study. By age 13, he was experimenting with lab-number generators, simple computers, powerful pneumatic rifles and telephone-answering machines.

Strangely, though, these gadgets began disappearing from the lockers where McClung and his friends stored them overnight. Kevin suspected that the thieves might be the turtle-necked, Ray-Banned adults who sometimes silently observed the kids at work. To find out, he embedded audio components into a neoprene wet suit, which he put on underneath his clothes. Then, he sidled up to the teacher’s office to eavesdrop on the visitors.

McClung was caught and his equipment confiscated, but not before he overheard one of the observers say: “The Agency’s got over 200 scientists, but most of them’ve been in the bull pen for 20 years. They’re stale. These kids are pure; they’re liable to come up with things our people’d never think of.�

About a decade later, while working for a Silicon Valley weapons contractor, McClung sees a near-replica of his body-hugging neoprene eavesdropper in a classified CIA catalogue illustrating surveillance equipment available to operatives. The mysterious visitors of his school days, he discovers, were actually government agents scouting out promising spy technologies as well as bright kids for possible CIA recruitment.

In “Dark Genius,� this seemingly made-in-Hollywood story is presented as a clear-cut tale of exploitation, but McClung is actually anything but a passive participant. He admits that he was drawn to the weapons contractor (referred to by the pseudonym Amida ) because he knew its real name referred to an ancient Chinese cult of assassins. And he is thrilled to discover that Amida’s founders may be working in covert intelligence.

Amida supposedly sells police products, but its ambitions are in the high-tech end of international arms trade. Soon after hiring McClung, they ask him to craft their first signature product: a fountain pen that can fire either a projectile or a toxin.

McClung’s creation is based on a much less lethal, silent and versatile Iranian version supplied by a consummate middleman named Abe Haddad. Haddad gives the pen to Amida’s leaders in the hope that they will reciprocate by involving him in their new business. Later, McClung is put to work designing such prototypes as a remote detonating device, which is sold to Col. Muhammar Kadafi. The company also supplies untraceable semiautomatic rifles, grenade launchers and shoulder-fired rockets to South African security forces as well as to right- and left-wing rebel groups, mercenaries and drug dealers.

Amida is nevertheless on the verge of bankruptcy, for Haddad and other middlemen have been promising product orders they don’t have, while Amida is guaranteeing weapons it hasn’t yet designed. (The latter practice is now so common in Silicon Valley that the hypothetical products have been given a name: “vaporware.�)

McClung and his co-author, Stephen J. Rivele, are comfortable using some real names--among them, Reagan’s national security adviser, Richard Allen--but the main characters and companies in their story are unacknowledged pseudonyms. Why? In his preface Rivele states that “a mentality . . . designed programs so illegal and immoral that they had to be concealed not only from the public but from the very government officials who were supposed to be in charge of them. This chronic secrecy has compelled me to fictionalize parts of this story . . . “

Nevertheless, the authors’ disguises are thin--Abe Haddad, for example, is clearly Albert Hakim of Contragate fame, while Intellicom is Tactronix--and their decision to mingle fact and fiction only diminishes the moral force and historical value of their book.

Are the tales told here credible? There’s a sloppiness in this text that gives one pause. For example, Amida’s offices in downtown San Jose are said to have “a view overlooking the soft brown hillsides of the the San Joaquin Valley.� They mean the Santa Clara Valley.

Yet around Silicon Valley one can find confirmation of some of this book’s most seemingly preposterous stories. Sworn depositions by Albert Hakim in a Tactronix lawsuit, for instance, provide ample parallels for their allegations about Intellicom.

Probably McClung plays loosest with the facts when posing as an innocent. Rather late in his tale, as he’s designing high-tech thumb screws and electrical shocking batons, Kevin “discovers� that he’s surrounded by “crass profiteers and mean-spirited opportunists.� “Dark Genius� is thus framed as a contemporary “Treasure Island�--as if Kevin is a Jim Hawkins who only discovers John Silver’s crooked nature once they’re both at sea. While Hawkins overhears the pirates plotting while sitting at the bottom of an apple barrel, McClung taps his boss’ office and discovers their plans to fire him because they feel they can no longer afford him or his changing attitude.

But Kevin is closer in character to the pirates than to Hawkins. Drawn to Amida because of an obsession with pistols, cutlasses and cannonballs, he wants to experiment at the edge of lethality without worrying about limits imposed by ordinary minds and morals. His obsessive drive is supported by a cold technological Darwinism persuading him not to waste pity on people weak enough to become targets.

After Amida’s various attempts to entrap McClung fail, he hides out for two years in the Sierras, where he has “mystical� insights about the sanctity of life. Readers are lucky that these insights led to a book-length confession, but the piercing strength of his epiphanies becomes suspect when we read the biographical note about his current occupation: “Kevin McClung owns a business in central California manufacturing custom knives and guns.�