This was the big question in international affairs for several years, and now that China has actually succeeded in detonating if not a deliverable bomb, at least ""a nuclear device,"" a carefully thought-out study of ""The Implications for American Policy"" could scarcely be more timely or more valuable. Mr. Halperin certainly seems to have considered every possible contingency within the covers of this slim volume. As foreseen by many authorities, the signing of a limited test ban detracted significantly from the propaganda effect of China's feat; but still, in this author's estimation, one of the larger dangers inherent in the situation could be the impetus for a proliferation of nuclear forces, with all the greatly increased difficulties of international control that would ensue. Chinese alternatives of aggressive and defensive action are meticulously analyzed, as are each of our various possible reactions, both in terms of immediate conditions and long-range eventualities. No one program is touted as ""better"" or even more likely, since Mr. Halperin is no sort of partisan; instead, he has begun the important work of charting the maze from which policy will eventually emerge.