The best nuclear book for the layman; The Fate of the Earth, by Jonathan Schell. New York: Avon Books. 244 pp. $2.50.

No other book on nuclear arms speaks as clearly or as sensitively to the layman, or encompasses the cultural, moral, and spiritual as well as the technological and political considerations that Schell's does. Most of us realize there would be no ''winner'' in a large-scale nuclear exchange; both sides would experience devastation unparalleled in history.

In the first of the book's three sections, Schell explores basic questions from the standpoint of an intelligent, inquisitive, and sensitive journalist. Part 2 of the book deals with human values, the meaning of possible extinction, and the differences between a catastrophe like the Nazi Holocaust and the potential loss of the entire human species. In Part 3 Schell examines the choices we have to face if we're to lessen or remove the nuclear threat. He stops short of proposing any political solution of his own but suggests that the task of finding one needs to be at the top of mankind's agenda.