NONFICTION : MODERN DRAMATISTS: BERTOLT BRECHT by Ronald Spiers (St. Martin’s: $19.95; 190 pp., illustrated). : MODERN DRAMATISTS: TENNESSEE WILLIAMS by Roger Boxill (St. Martin’s: $19.95; 186 pp., illustrated).

St. Martin’s Press is introducing its Modern Dramatist Series by focusing on two diametrically opposed playwrights. Bertolt Brecht and Tennessee Williams changed the face of 20th-Century drama, but there the similarity between them ends, both in form and content.

Senior editors Bruce and Adele King chose Ronald Spiers, who wrote an earlier Brecht study, and teaches at the University of Birmingham, to profile Brecht. Roger Boxill, a journalist and English professor at New York’s City College, writes on Williams.

Brecht was an ideologue who fashioned drama according to his own philosophical lights, but according to Spiers achieved some of his greatest effects despite, not because of, his theories.

Still, what worked for Brecht and Williams was how they were able to make real their world-views. Brecht not only perceived the world from a dedicated dialectical materialist perspective, he sought to create a new kind of theater in which even the process of producing the play was a revolutionary act. You don’t understand much about Brecht, whose best known work in this country is “Three Penny Opera,” unless you know he was a German Communist who fled Hitler, ending up an exile in Los Angeles where he worked on “Galileo” and “The Caucasian Chalk Circle.”

You don’t understand Williams without knowing that he was a homosexual with an essentially Freudian viewpoint, the scion of a shabby-genteel Southern family.

To Williams, the reality is that everything is decay and impermanence. Human lives burn brightly for only a fleeting second, and the rest is entropy of the most grotesque sort.

Williams, says Boxill, was a particularly modern dramatist, whose work transposed easily from stage onto screen. That’s why, he suggests, so many of his works--including “The Glass Menagerie,” “Night of the Iguana,” “A Street Car Named Desire,” “The Rose Tattoo,” “Sweet Bird of Youth” and “Cat on a Hot Tin Roof”--worked well as films.

The books combine biography with a blow-by-blow description of the themes, theories and history behind the plays. That way, the metaphysics underlying the work of each dramatist is plain to see and compare. Series volumes on Edward Albee, Gilbert & Sullivan, David Mamet and Noel Coward are due soon.