Star Warriors: The Young Scientists Who Are Inventing the Weaponry of Space by William J. Broad (Simon & Schuster: $16.95; 236 pp., illustrated) : THE MILITARIZATION OF SPACE: U. S. Policy, 1945-84 by Paul B. Stares (Cornell University: $25; 334 pp.)

It’s fascinating how two books on roughly the same subject can be so completely different. William J. Broad and Paul B. Stares have produced two excellent books on weapons in space--with no overlap whatsoever.

Both present their material chronologically, with each chapter representing a period of time dominated by an individual. In “Star Warriors” by Broad, the period of time is a day in his visit to the Lawrence Livermore Laboratory, and the individuals are young scientists involved in the development of “Third-Generation Nuclear Weapons” for “Star Wars.” In “The Militarization of Space” by Stares, the period of time is a number of years, and the individual is at every point a President of the United States trying to cope with the possibility of an arms race in space. Broad’s book covers one week; Stares’ covers four decades.

The subject of both books is space weaponry. Yet one would be hard pressed to find a single system that is mentioned in both books. “Star Warriors” by Broad deals in the weapons of the future, while Stares documents those of the past. And while both authors recognize the existence of a relationship between the two, Broad concentrates on “Star Wars” (satellites to shoot down missiles), while Stares emphasizes ASATs (missiles to shoot down missiles).

The biggest difference between these two books is in their style. Broad’s book is intimate, even gripping. It reads like a good novel. He makes the characters come alive--all of them, from a historical giant like Edward Teller to the ex-fiance of one of the scientists in the lab. And he makes you care about them. Like the good journalist that he is, Broad gets inside people. He discovers and reveals to the reader not only what people do and say, but why . Broad seems to understand that it is almost impossible to judge a proposal (whether for a trillion-dollar weapon system or for a thousand-dollar used car) without knowing the underlying motivation. By revealing the mentality of those selling “Star Wars,” Broad has made an important contribution to the public debate.

Where Broad really shines is in his ability to make science interesting. Unlike many science popularizers who oversimplify complex phenomena and turn then into pseudo-science, Broad serves up the real thing. Though explained in such a way that it is easily understandable to the layman, his science is nonetheless correct.

In describing a laser, for example, Broad says, “What makes the bursts so special is that they are coherent; that is, they are made up of radiation whose waves are all in step with one another.” And he describes a laboratory laser experiment this way: “What was about to happen was the creation of an intense pulse of visible light--but one that was very special. Regular light is made up of electromagnetic waves of many different frequencies and phases that often interfere with one another, just as waves on the ocean surface often cancel each other out. In contrast, waves of laser light have exactly the same frequency and direction of motion and are perfectly in step with one another. They are a pounding rhythm of light.” By comparison, Robert Jastrow in his recent book devoted a whole chapter to explaining lasers without even mentioning coherence. Broad is to be congratulated for not trivializing his science.

Stares’ book, on the other hand, is as clinical as Broad’s is intimate. Stares is a scholar (a very good one) and his book reflects that. It reads a bit like a Ph.D. thesis, which shouldn’t be surprising, since that’s essentially what it is. It is also a treasure trove of information. The appendices alone are worth the price of the book to anyone interested in space weapons. The very day I received the book in the mail, I referred to it for data on Soviet anti-satellite (ASAT) tests to confirm my answer to a congressman who was preparing a floor speech for that day.

Though I later read it from cover to cover, very few who buy the book will ever do so unless they enjoy drinking from a fire hose. This is meant as a caution, not a criticism, for the book is actually very well written. Of course, so is the Encyclopaedia Britannica. Like the latter, the greatest value of this book will be as a reference. Anyone interested in space weapons, arms control, or U.S.-Soviet relations will probably be reaching for it a lot.

With all their great differences, the two books wind up with similar conclusions. Stares says, “The advent of anti-satellite and other space weapons will be akin to opening the mythical Pandora’s box. The putative benefits of such weapons will be short-lived or, more likely, illusory. Instead, the superpowers will become locked into a never-ending, ever-demanding search for security in space that will leave them worse off than before.”

At the end of his intensive investigation of “Star Wars,” Broad concludes, “Using it for anything other than a bargaining chip seems pure folly. A week of conversations at the lab convinced me that the assertions of the critics are generally correct: A move to defense would touch off an expensive new arms race that would make the world a more dangerous place in which to live.”

As different as bread and wine, these two very intelligent, extremely informative books go well together. If one is a little dry, take it for its substance and sip the other for enjoyment.