JEAN-PAUL SARTRE, whose first novel, ''Nausea,'' had a biographer as its hero, spent the last 10 years of his working life on a massive psychobiography of a writer he had always detested for his estheticism and his reactionary opinions - Gustave Flaubert. He customarily explained this curious project as an attempt to synthesize what can be understood today about an individual life, given what we have learned from a century of work in psychoanalysis, social psychology, linguistics, anthropology and the symbolic analysis of culture and individual behavior. But for Sartre, understanding always involved the discovery of that point at which all constraints - external accidents, the miseries of psychic determinism and social conditioning - are suddenly transformed into the active gestures and free choices of an individual - what he called ''praxis.'' It is never easy to reach that magical point. ''The Family Idiot'' takes some 3,000 pages to get there.
This vast work is now beginning to appear in a splendid translation by Carol Cosman. There are four more volumes scheduled to appear in the next eight years. Simultaneously with this first volume the University of Chicago Press is publishing a study by Hazel Barnes in which ''The Family Idiot'' is recapitulated in its entirety. Her summary is very useful, for this last work of Sartre's is marked by an exasperating prolixity. Blindness forced him to abandon the final volume, which was to have been an analysis of ''Madame Bovary.'' Miss Barnes's study not only provides a quick preview of the whole work, but it gives for the first time anywhere an account of Sartre's notes for the final, unwritten volume.
Sartre called ''The Family Idiot'' a ''true novel,'' and it does tell a story and eventually reach a shattering climax. The work can be described most simply as a dialectic, which shifts between two seemingly alternative interpretations of Flaubert's destiny: a psychoanalytic one, centered on his family and on his childhood, and a Marxist one, whose guiding themes are the status of the artist in Flaubert's period and the historical and ideological contradictions faced by his social class, the bourgeoisie. But there is no determinism in his approach, for Sartre insisted on seeing contradictions - whether psychic-familial or socio-economic - as so many situations for which we cannot but invent responses: ''Neurosis,'' as he says in an earlier work, ''is an original solution the child invents on the point of stifling to death.''
In his Marxist interpretation of Flaubert's situation as a young bourgeois artist in the middle of the 19th century, Sartre articulates two levels of dilemma: the crisis of the serious middleclass artist in a marketsystem, faced with a disappearing audience; and the ideological crisis of the French bourgeoisie, which during the French Revolution had invented the notion of a universal human nature as a weapon against the aristocracy, only to find itself confronted in the days of the 1848 revolution with a new proletarian underclass it was reluctant to recognize as part of that universal humanity. The bourgeoisie will ''solve'' this new problem by becoming Victorian, by repressing the animal and physical ''nature'' it seemed to share with the proletarians and by transforming its earlier humanism into a misanthropic positivism.
The bourgeois artist faced additional problems. As commoners, Flaubert's generation could no longer enjoy the metaphysical confidence of the earlier aristocratic Romantics like Chateaubriand, whose ''genius'' and ''suffering'' expressed a whole class's repudiation of the new middle-class business world. And the revolutionary vocation of the the great bourgeois writers of the Enlightenment was also denied them, precisely because those writers succeeded in overthrowing the ancien regime. Yet Flaubert's generation was formed by the works of both these preceding literary generations.
Sartre here develops a theory of generational ''misprision'' (or misreading), drawing on the concept of the ''practico-inert,'' which he had developed in his ''Critique of Dialectical Reason.'' Sartre had always seen literary works as responses to concrete situations, responses that become intelligible only when grasped within those situations. He now draws the unexpected consequences: Like tools, literary works outlive the situations for which they were intended, and they are passed down with a new material inertia. ''The tradition of all the dead generations,'' Marx said, ''weighs like a nightmare on the brain of the living.'' The artists of Flaubert's generation had no way of understanding the practical purposes for which the older generation had invented their now inert themes: critical negativity, misanthropy, the ideal of classlessness, the defense of the autonomy of the intellectual (which will now be ''mistranslated'' as art for art's sake), and a quasi-religious conviction of the nothingness of the world and the emptiness of life. Crippled by the themes of their predecessors, the following generation became artists without inspiration. This was not a subjective matter, a lack of talent or vocation. Rather, Sartre's idea of the practico-inert -the weight of so many dead artistic ideologies from an incomprehensible past - suggests a situation in which it was objectively impossible for them to have something to say.