Collection of Sontag's work; A Susan Sontag Reader. Introduction by Elizabeth Hardwick. New York: Farrar, Straus & Giroux. 446 pp. $17.95.

Here is a selection from 20 years' work by the novelist-critic who has been called ''our most celebrated woman intellectual.'' The contents include Sontag's most famous essays (''Against Interpretation,'' ''On Style''); the random musings presented as ''Notes on Camp''; several short stories, plus excerpts from her two novels; a discussion of how the camera ''usurps reality''; part of a long interview previously published in ''Salmagundi''; and her profile-introductions to the work of writers she particularly admires, such as the critics Walter Benjamin and Roland Barthes.