King Richard III. Tragedy by William Shakespeare. Directed by Jane Howell. The 28th season of free Shakespeare in Central Park has opened with a headlong, turbulent, four-hour revival of caca''King Richard III.'' With Kevin Kline's sharply intelligent portrayal of the king - Shakespeare's monster villain - setting the tone and pace, the production, which is directed by Jane Howell, transforms the Delacorte stage into an arena of political chicanery and murder. It is a world described by the doomed Lord Hastings as a ''momentary state of worldly men,/Which we more hunt for than the grace of heaven!''
The ruthless mover and shaker in these particular power struggles is, of course, the Duke of Gloucester (later Richard III). Hamlet said that ''conscience does make cowards of us all.'' Not so with Richard. In his opening soliloquy, King Edward's youngest brother announces his villainy, rationalizes it by referring to his deformity, and explains quite matter-of-factly the first of the plots he has laid.
Richard expounds villainy as a policy. It comes naturally to him. He mocks his victims with sardonic asides even as he is making his outward avowals of loyalty, piety, righteousness, and other moral virtues. Richard even manages to turn ex-Queen Margaret's celebrated curse against her - no small feat considering the kind of spine-tingling delivery it receives from Marian Seldes.
Richard's devious successes must, in performance, spring from the histrionic adroitness of the actor who plays him. In this demanding feat of make-believe, the usurper's very lack of all moral scruple becomes the spectactator's cause for astonishment and fascination. Mr. Kline possesses the art to make Richard's unbelievability believable. This Richard can even manipulate Lady Anne (Madeleine Potter), whose husband and father he killed, into marrying him.
And therein lies one of the moral themes of ''Richard III.'' At a certain point in many an aggressive scheme, the aggressor's success results from a kind of complicity or at least irresoluteness on the part of the victim. The case of the politic Buckingham (Gerry Bamman), Richard's hatchet man, illustrates two aspects of the moral disorder that occupies ''Richard III.'' His momentary scruple over arranging for the murder of Richard's two little nephews costs Buckingham his preferment and indirectly his life.
Almost inevitably this ambitious New York Shakespeare Festival is not all of a piece in terms of achievement. But the strengths of the performance predominate. They include the austere majesty of Betty Miller's beautifully spoken Duchess of York, the straightforward innocence of Bruce Davison's Clarence, the quiet sinisterliness of Christopher McCann's Ratcliffe, the unwary trustfulness of John Seitz's suddenly entrapped Hastings, and the poignant maternalism of Concetta Tomei's Queen Elizabeth.
The incidental martial movements are well handled while the climactic battlefield encounter between Richard and Richmond (David Alan Grier) has been staged by B.H. Barry with his flair for the spectacular. Composer Richard Peaslee's percussive motifs and horn flourishes underscore the mighty struggles they accompany.
The theme of Miss Howell's concept is the mortality of temporal power. The war-ravaged milieu of 15th-century England is suggested by designer Santo Loquasto's murkily painted curtains, which serve both as backdrops and enclosures - all atmospherically lighted by Pat Collins.
The Central Park ''Richard III'' makes heavy demands on its actors as it unfolds, with remarkable clarity and exciting thrust, Shakespeare's complex tale of villainy and treachery in high places. The result is admirably well worth the effort. The production runs through July 31.