Plight of 1920s blacks superbly portrayed in new Wilson drama; Ma Rainey's Black Bottom. Play by August Wilson. Directed by Lloyd Richards

The time is 1927. The place is the band room and recording studio of a Chicago record company. Under the prevailing practice of the time, the firm's ''Race'' division puts out discs by black performers aimed primarily at the black audience. As the curtain rises at the Cort Theatre, the bleak, utilitarian premises await the arrival of singer Ma Rainey and her four musicians.

After some introductory wrangling between Sturdyvant (John Carpenter), the studio owner, and Ma's manager, Irvin (Lou Criscuolo), the musicians begin drifting into the studio. The four men project their highly individual personalities as they thrash out their disagreements and express their views on a variety of matters. They even do a little rehearsing. The quartet consists of easygoing bassist Slow Drag (Leonard Jackson), philosophical and bookish pianist Toledo (Robert Judd), drivingly ambitious trumpeter Levee (Charles S. Dutton), and fatherly trombonist-leader Cutler (Joe Seneca).

The tardy arrival of Ma Rainey (Theresa Merritt) galvanizes the situation and introduces a whole new dynamic. The imposingly temperamental blues diva disdains a trailing policeman and leaves it for the harried Irvin to deal with the consequences of a traffic mishap. Miss Merritt creates a massively imposing figure of a black prima donna determined to preserve the integrity of her music. Ma is totally realistic about her importance to and relationship with the exploiting white establishment, represented by the hard-nosed Sturdyvant and the placating Irvin. Among other things, she insists that her stuttering nephew (Scott Davenport-Richards) deliver the short, spoken introduction to ''Ma Rainey's Black Bottom.''

While Ma Rainey supplies the dominant bravura figure of Mr. Wilson's drama, the play's primary focus is on the life and times of the instrumentalists. The central figure of the band room is the volatile Levee. An obsessively ambitious player-composer, Levee wants to experiment with new jazz forms, write his own songs, and have his own band. Boastful and aggressive, he wastes no time in making seductive advances to Ma's willing young companion Dussie Mae (Aleta Mitchell). The careerism of a small musical world becomes the instrument and metaphor for Mr. Wilson's larger purpose: a troubling examination of the black citizen's plight during one of the most virulent periods of American racism. Cutler recounts the harrowing tale of a stranded black minister bullied and humiliated by some Georgia ''crackers.'' Levee recalls the even more horrible childhood memory of his mother's being gang-raped by whites and of the fatal consequences of the crime.

The recollection helps trigger the unintended killing with which Mr. Wilson climaxes ''Ma Rainey's Black Bottom.'' For all the explosive violence of its somewhat calculated finale, the substance of the work is filled with deep insights as well as with spontaneous humor and delight, delivered in what, to a white spectator, seems an authentic idiom.

The acting is superb throughout. In the performance staged by Lloyd Richards, each of the musicians is vividly individualized. Miss Merritt's Ma Rainey is larger than life and twice as impressive - the very personification of the living legend once known as ''the mother of the blues.'' The admirably mounted Yale Repertory Theatre production was designed by Daphne Pascucci (costumes), Charles Henry McClennahan (setting), and Peter Maradudin (lighting). Dwight Andrews provided the musical direction for the numbers that helped capture the mood, tenor, and tempo of a turbulent era.