India, second most populous nation in the modern world, is a country too few Americans know anything about; and Pandit Nehru, the man most responsible for the roles India has taken upon herself today, is almost equally complex and mysterious. This work of sympathy, praise, and measured criticism, by an Englishman with a long acquaintance with both the man and his land, is therefore very welcome. Mr. Tyson denies any claims to the title of biographer, definitive or otherwise, and calls his book merely ""an attempt to assess the years of power"" -- the 17 years from 1947 to his death when Nehru was prime minister and prime mover of India. Foreign affairs, the policy of nonalignment and the disputes with Pakistan and China necessarily loom large, but it is internal matters, how Nehru sought to apply his form of socialism and to reconcile the problems of an infinitely diversified ethnic and social structure, which will be least known and probably of most interest to the American reader. Mr. Tyson has made all this comprehensible and yet not overly simplified.