New York The uptown Circle in the Square Theater is having another try at the classics. The Circle's Broadway season began with an assault on Shaw in a misguided version of ''Candida.'' Now comes an earnestly conceived yet less than enthralling ''Macbeth,'' a revival in which Nicol Williamson serves as both director and leading player. In the current fashion, Williamson seeks to create a timeless but vaguely antique context for this tragedy of dark deeds and darker thoughts. Most of the male characters are dressed in metalesque tunics, riding breeches and boots, and sport sabers. The women wear long gowns. The Christian moral order the Macbeths defy is suggested at the outset -- by a prelude of liturgical organ music and by a large, centrally placed Celtic cross that is removed in time for the three witches to take their stations. Ecclesiastical symbols recur periodically in the course of the action, continuing right through the final, frenzied confession by the murderous usurper who has ''supp'd full with horrors.'' Williamson's Macbeth is an upright and victorious general, quickly and irretrievably corrupted by his own ambition, the weird sisters' predictions, and Lady Macbeth's eager complicity. He perceives, from the outset, how ''the instruments of darkness tell us truths,/Win us with honest trifles, to betray's/In deepest consequence.'' Macbeth never achieves the clearness he seeks. Instead, he plunges further into murders to shore up his own vulnerability. At last, precipitously seated on a shaky throne, he is broken by the moral order he has tried to break. In his concept of the relationship between Macbeth and Lady Macbeth (Andrea Weber), Williamson apparently sought to contrast the complexities of Macbeth with a Lady Macbeth of almost girlish impulse and -- in first instance -- of simple, reckless pragmatism. The concept doesn't work out in performance, mostly because the attractive Miss Weber lacked the experience and emotional maturity for the part. The Circle in the Square revival suffers from yet other inadequacies. There is almost no sense of majesty or occasion to this crime drama in high places. The prevailing tone is middle-class egalitarian. The three weird sisters (Elaine Bromka, Bette Henrize, and Tara Loewenstern) do, however, create the requisite atmosphere of the witchcraft that entices Macbeth with prophecies whose ambiguous meanings he perceives too late. By telescoping the tragedy's five acts into one uninterrupted continuity, and by some incidental cutting, Williamson has achieved a smooth performance that runs about two hours. At a final preview, this method did not seem to add appreciably to the play's pace or impact. The supporting cast includes John Henry Cox (a forthright Banquo, Joyce Fideor (a touching Lady Macduff), J. T. Walsh (Macduff), Tom McDermott (Duncan), Ray Dooley (Malcolm), and Paul Falzone (Ross). Helpful performances in smaller roles include those of Paul Perri (Seyton), Peter McRobbie (the Doctor), and Miss Bromka (the Gentlewoman). The spare production -- a flagstone playing area leading to a stairway and two murky towers -- was designed by Kenneth Foy. Julie Weiss costumed the revival, William Armstrong lighted it, and the incidental music is credited to Guy Woolfenden. — Tragedy by William Shakespeare. Directed by Nicol Williamson.