IN AN AGE when words like fission, double-helix, and plutonium are on the tip of every layman's tongue, books about science, or better yet books by scientists, are a sure sell.

On a bad week, four out of the top ten books on the Times best seller list qualify as "science books." And most bear the birth-defects of their accelerated delivery--some are sensational, some scientifically irresponsible, others just badly written.

Freeman Dyson's first book, Disturbing the Universe, has all the trappings of a commercial pounding: his famous name, sensational subject matter, characters from history books. But Dyson, who might have gotten away with a forgettable rehash, offers instead a captivating portrait of one of the formative minds of modern physics--his own.

We meet Freeman Dyson as a nine-year-old child poring over--not Einstein's differential equations--but Edith Nesbit's utopia. This introduction is true to character. Dyson is not just a physicist; he's a romantic, a humanist and an optimist.

If Disturbing the Universe is a fair indication, Dyson spent the first twenty pages of his life as a child, the next eighty as a pure scientist, and the bulk of it, the final 150, as an ill-defined political spokesman, a defender of this and a believer in that. For the middle eighty pages the book soars. This is where we find what we came for: a candid description of the remarkable collaboration between Dyson's mathematical genius and his imagination, or the even more remarkable collaboration of his gifts with the complementary ones of those around him.

BUT ALL TOO SOON he shifts to a more familiar realm--the political applications of science. To his credit, Dyson shies away from no controversial issue: England's strategies during World War II, nuclear warheads, the possibility of biological warfare. In each case, Dyson gives his exacting rationale for the stances he has adopted. His conclusions are always responsible, often noble, and occasionally naive. For instance, he ascribes our failure to develop safe nuclear reactors to contemporary scientists' inability to have fun inventing them. And as a solution to the energy crisis, he proposes that we somehow clone trees to yield gasoline.

If the first half of Disturbing the Universe is largely his scientific autobiography, the second is his somewhat disjointed account of what must have been a disjointed later career. Why should a man of such acknowledged brilliance lead his professional life thus--first working with atomic energy, then space missions; now testifying before the Supreme Court, now tutoring the Princeton prodigy who independently discovered the atomic bomb? Because, it seems, he gave up on himself as a pure theoretical physicist. "I was," writes Dyson, "and always have remained, a problem solver rather than a creator of ideas. I can not, as Bohr and Feynmann did, sit for years with my mind concentrated on one deep question."

This portion of the book accounts for the most puzzling disproportion in Disturbing the Universe. Freeman Dyson is a proven scientific commodity. Robert Oppenheimer hailed his successful synthesis of two seemingly irreconcilable but equally correct theories of the electron as one of the century's breakthroughs. Now the Alfred P. Sloan foundation has asked him to contribute his bit to "the public understanding of the scientific enterprise."

But what Dyson has written reads at times more like a confession. In Disturbing the Universe, science is often secondary to Dyson's enunciation of his personal failures and vulnerabilities. This is the most unexpected and endearing aspect of this unorthodox book. But while Dyson is eloquent, he is not a professional writer when he picks up a pen and bravely sets down what means most to him, he is not always convincing.

Dyson carries on a crusade against the English and then the American bureaucracy throughout the book. His preoccupation with this issue was born of his work as a researcher for the English government during World War II. His criticism extends to the American bungling of arms control. Dyson argues that the United States should have abandoned offensive-weapon research in favor of defensive-weapon research. He expresses admiration for Richard Nixon's unilateral decision that the United States should abandon the use of biological weapons.

Behind this action lay his scientific hero--Matthew Meselson, who inspired Nixon's move. And it is for him that Dyson reserves his greatest praise. "Seldom in history has one man, armed only with the voice of reason, won so complete a victory," he says. And Meselson is not the only of Dyson's heroes. There's Frank Thompason, the idealistic poet, who went down in action in Yugoslavia, a political hero fighting for a noble cause; there is the humble black woman who served with Dyson on a committee to decide if DNA research was to be allowed at Princeton; and lastly there's his own son, who makes canoes in British Columbia, and whom Dyson saw save two lives in a way that contrasted sorely with the rankling memory of his own inability to do the same many years ago.

THE LAST SECTION of Disturbing the Universe unveils Dyson's far-reaching ideas for the future. "I am obsessed with the future," he writes, and then offers the imaginative products of this obsession: clades and clones, interstellar colonizations and "thought experiments." There is even a little theoretical physics. But this is the weakest part of the book. It is more science fiction than science.

The book is a gripping journey to another mind, active, but obsessed; too bright, but not bright enough. It is a nice place to visit, but you wouldn't want to live there.