Samuel Beckett, by Deirdre Bair. New York: Harcourt, Brace, Jovanovich. $7 .95.

This blockbuster biography is the best introduction to an enigmatic giant of 20th-century literature. While Beckett said he would neither help nor hinder Bair's efforts, she has produced a fat book about a singularly spare man, getting much of the meat from a cache of about 300 letters Beckett wrote to his friend Thomas McGreevy. More of a book for dipping into than reading straight through, but a major accomplishment nonetheless.