STAR WARRIORS: A Penetrating Look into the Lives of the Young Scientists Behind Our Space Age Weaponry. By William J. Broad. Simon and Schuster. 245 pp. $16.95.

THEY LIVE on peanut butter, ice cream and Coca- Cola. They stay up all night toiling at their computers. They don't know any girls. For an aficionado of apocalyptic movies, it is a great disappointment to learn that the real architects of global doom are not grinning Doctor Strangeloves but sun-starved wonks addicted to sugar and caffeine.

The Star Warriors of William J. Broad's title are youthful physics prodigies from Cal Tech and MIT who design particle beams, X-ray lasers and "brain bombs" at California's Lawrence Livermore National Laboratory. Founded in 1952 primarily through the efforts of Edward Teller (father of the H-bomb, eangelist of the arms race and generally one of the 20th century's premier troublemakers), Livermore is the nation's number-two nuclear weapons lab and the birthplace of Ronald Reagan's "Star Wars" fantasy. Under Teller's inspirational gaze, the star warriors hammer out designs for the nuclear weapons that the president says will eliminate the need for nuclear weapons.

Broad, a science writer for The New York Times, introduces his subjects as "anything but humorless automatons," then proceeds to describe a group of humorless automatons. This is partly their fault, partly his. Most of the young scientists seem to have spent their adolescences earning PhDs; few have interests beyond the keyboards of their computers. One of them, a 31- year-old MIT graduate named Rod Hyde, frets that the Soviets will take over the world before he can blast off for the stars in a spaceship he's designing on the side. "I'm more or less convinced that one of these days we'll have World War III or whatever," says one of Hyde's colleagues. "It'll be pretty ugly. A lot of cities will get busted up." These are characters that are not, to put it mildly, Shakespearean in their dimensions.

Broad's reporting style doesn't help. His portraits are flat, his narrative is disconnected, and his journalistic curiosity is anything but insatiable. Many promising topics get a "Science Times" once-over and then disappear. Part of the problem is the week-in-the-life format in which he has chosen to organize his material. Since nothing much happens during the seven days he is on the premises at Livermore, much information has to be filled in during contrived asides in which, for example, Broad sits under a tree and "thinks about" Teller's past. Star Warriors reads like an interminable newspaper feature story occasionally sprinkled with editorial-page profundities ("Was it man creating innovative tools or had the evolution of technolog somehow gotten out of hand and made humanity its slave?").

The most interesting of the star warriors is Peter Hagelstein, a brilliant 29-year-old who came to Livermore hoping to win a Nobel Prize for inventing the world's first X-ray laser, a device that he believed would prove invaluable in medical research. But gradually Hagelstein realized that the only way he could continue his work was to concentrate on the laser's potential as a weapon. Originally appalled by the thought of designing bombs, he eventually provided the breakthrough that led to the first serious formulation of Star Wars.

"Writers of science fiction are supposed to look into the future," Hagelstein told Broad. "So I started looking to see what they had in mind for X-ray lasers. It turns out that all the science fiction references are to blowing things up." Hagelstein's conversion cost him the affections of his girlfriend and also, one infers, a certain measure of his peace of mind. Still, he apparently decided that tainted research was better than no research at all.

As is also true of many of his colleagues, Hagelstein's ticket to Livermore was a generous grant from the Hertz Foundation, a private organization with close ties to Livermore (Teller sits on its board) that was established by rental-car magnate John D. Hertz. The foundation has been accused of covering up its weapons connection in order to lure innocent young minds into the bomb business. Broad tiptoes around this story but never digs in. As in his portrait of Hagelstein, whose motivation remains elusive, he suggests much more than he explains.

Broad does succeed at conveying some of the eager self-deception that apparently fuels the bomb- makers. The Livermore kids downplay the uncertainties of the technology they're tinkering with in order to win more time at their beloved computer consoles. Untenable assumption is piled upon untenable ssumption. Would orbiting laser platforms be vulnerable to Soviet attack? Okay, we'll launch the lasers from submarines. Would submarine launchings take too much time? Okay, we'll put the lasers on orbiting platforms. One cocky young scientist answers Star Wars critics by claiming that shooting down missiles with as yet unbuilt laser bombs would be child's play. "The space shuttle is a lot more complex than what we're doing," he tells Broad. "An automobile is more complex. Have you ever looked under the hood of an auto?"

Benjamin Franklin thought hot air balloons would make war impossible; the Wright brothers believed the same of airplanes. What do the star warriors believe? Some apparently share at least part of the president's goofy faith in their ability to make World War III impossible. But most seem quite cynical in their explanations for what they do. A remark by Hans Bethe, a director of the Manhattan Project and an outspoken critic of Star Wars, seems on the mark: "The young people wat to show something for themselves. Yet many, many people in the nuclear weapons enterprise have stated that there isn't much more to be done about offensive weapons. So, they say, 'If we want to continue in this field, let's try defensive weapons.'" In major-league nuclear physics, Star Wars is the only game left.

There isn't much the ordinary person can do about the prospect of nuclear war except discover new reasons to worry about it. Star Warriors, for all its many shortcomings, provides plenty of those.