''After the Fall,'' at Playhouse 91, is a drama about a successful lawyer whose failures in marital and other relationships bring on feelings of doubt and self-recrimination which he seeks to exorcise through a kind of confessional process. This semi-autobiographical Arthur Miller work was a troubled and troubling play when first presented in 1964. Two decades have moderated some of the sharpness of its references. But as is often the case with confessions, this one can make the listener feel uncomfortable even while it is absorbing him.
Mr. Miller casts the audience in the role of a confidant, whose attention lawyer Quentin (Frank Langella) seeks to engage as a friendly ear for his recital of personal crisis. Quentin reveals a greater capacity for shattering relationships than for sustaining them. Even his loyalties involve a tainted motivation. He says at one point: ''I am bewildered by the death of love and my responsibility for it.''
A series of flashbacks enumerates and specifies Quentin's failures. Private and public ordeals impinge on each other. Early scenes recall a traumatic childhood incident and his family's financial ruin in the crash of 1929. Former communists and fellow travelers from his law-school days become embroiled in congressional investigations. Quentin undertakes to defend a revered former professor, only to learn that the man has committed suicide.
On a more intimate level, ''After the Fall'' centers on Quentin's two failed marriages and particularly on his disastrous union with Maggie (Dianne Wiest), a psychologically fragile young woman who rises to stardom as a pop singer followed by alcoholism and fatal drug addiction. Although the role no longer requires the actress to wear a blond wig, the ghost of Marilyn Monroe still haunts ''After the Fall.'' To her credit, Miss Wiest gives a performance that encompasses Maggie's beguiling charm as well as the insecurities that embody her self-destructiveness.
Mr. Langella endows Quentin with a candor and appealing directness which, to a point, win the spectator's sympathy but do not altogether dispel suspicions of the character's disingenuousness. According to a program note, ''The action takes place in the mind, thought, and memory of Quentin.'' The recollections are by their very nature subjective, seen through a glass darkly. In his candor about himself, has Quentin been totally fair to others? One cannot know.
Even in a version that has been cut by about half an hour, ''After the Fall'' remains a long and complex play. It is admirably acted under John Tillinger's direction by a cast that includes Mary-Joan Negro (Quentin's first wife), Salem Ludwig and Tressa Hughes (his parents), and Laurie Kennedy (the woman he is courting).