MARAT SADE, director Peter Brook's film adaptation of the Royal Shakespeare Company's production of the Peter Weiss play, stars Patrick Magee as the Marquis de Sade. At an insane asylum in suburban Paris, de Sade leads his fellow patients in a reenactment of the murder of Jacobin luminary Jean-Paul Marat (Ian Richardson) by Girondinist Charlotte Corday (Glenda Jackson) at the height of the French Revolution, for the amusement of an upper-class audience 18 years after the conflict's end. Like the historical figures in the imaginary conversations of Walter Savage Landor, Marat and de Sade engage in an intense marathon debate on a variety of political and philosophical subjects. On violence, the revolutionary prefers that it be used in service of political ends, while to de Sade, it's strictly a matter of personal pleasure. This discourse of mandarin madmen is interspersed throughout with the antics of clownish inmates Kokol (Hugh Sullivan) and Cucurucu (Freddie Jones), a reminder of the play's confined setting. Whether a result of budget constraints or Brook's personal choice, this is clearly the film version of a stage production, but, unfolding in long, relatively seamless takes, this is not a distraction. In all, this is a high-powered, intellectual roller coaster, performed with manic intensity by the RSC, and featuring an astonishing debut by Glenda Jackson.