It is a question that reach reader must face and answer individually: how much of Bertolt Brecht should be kept readily available on a handy shelf. For minimalists, a handy answer is provided in Brecht: Collected Plays, Volume 2, edited by Ralph Manheim and John Willett (Vintage, $6.95). The two plays which constitute basic Brecht are placed side by side in this volume, with some of the author's notes at the end. They are, of course. The Threepenny Opera (1928) and Rise and Fall of the City of Mahagozny (1929). For Brechtians with larger appetites, Volumes 1,5.7 and 9 are also listed by Vintage, with more to come.

Those who have a taste for poetry and a smattering of German may wish to add at least the bilingual Manual of Piety (Grove, $2.45), and for those who wish to see the writer in his context, Bertolt Brecht's Berlin: A Scrapbook of the Twenties, by Wolf Von Eckardt and Sander L. Gilman is now available in paperback (Anchor, $5.95), offering a thorough, anecdotal and lovingly detailed survey in words and pictures of the city's golden years under the Weimar Republic.

All aspects of the city's life are covered, not only the philosophers, painter, musicians and Bauhaus architects who gave it special distinction, but the social unrest, the nightmare inflation, the glittering cabarets and low bars, the prostitutes, drug addicts and petty criminals who have a special bearing on the work of Brecht. The positive side of the picture is indicated by scanning quickly a partial list of the distinguished exiles who transferred some of the Weimar culture to the United States after Hitler's accession to power: Paul Tillich, Albert Mann, Bertolt Brecht, Kurt Weill, Lotte Lenya, Laszlo MoholyNagy, Mies van der Rohe, Walter Gropius, Paul Hindemith, Otto Klemperer.