AT THE ZOO, everybody likes the monkey house. The chimps clutch the bars and make faces; the orangutans lounge obscenely and scratch their hairy orange arms. With ape-like gestures, the cast members of the Mainstage production of Peter Weiss's Marat/Sade shriek, jabber and carry on. As the inmates of the asylum of Charenton, they perform a play within a play. The Persecution and Assassination of Jean Paul Marat, written by one of their own number, the Marquis de Sade.

Marat Sade thus presents a dual challenge to its cast--they must portray both lofty historical figures and loonies at the same time. The actors attack this problem with great skill, capturing the madness and hysteria of France's Reign of Terror as well as of the grimmer episodes of the 20th century. Directed by Maja Hellmold, this Marat/Sade suceeds in drawing us into an asylum that is a microcosm of our own crazy world.

Belle-Linda Halpern, who plays Charlotte Corday, the fiery young woman who stabs Marat to death is at the same time a groggy somnambulist who can barely wield a knife: she shuffles about in circles and slumps to the floor while delivering impassioned soliloquies. Funny yet frightening, pitiful yet majestic, Halpern's performance is haunting. Christopher Moore is the "lucky paranoiac" who gets to play Marat. Suffering from a skin disease, the feeble and pinched looking Marat crouches in a bathtub. His fervent speeches sound simultaneously noble and pathetic as he bleats them in a madman's wavering voice. Although sympathetic and believable, Moore lacks the personal force of a rabid activist. On the other hand, Nick Lawrence displays great haughtiness as the infamous Marquis, swaggering about and scorning the other inmates as "lost revolutionaries." During, his soliloquies, however, he seems too coldly contemptuous of political movements, too condescending towards Marat, and he enunciates with such precision and venom that his words sound forced.

In the difficult role of Corday's lover Duperet, Ben Evett is hilariously lewd, while Laurie Gallueto is equally effective in the role of Simonne Evrard, the head of Charenton, who tries to neal her patients through participation in art. At the same time, she is the censor of the play, who interrupts subversive talk and menacingly reminds the crazies that "everything is being done to alleviate sufferings." Pale and stone-faced, she makes the audience's blood run cold.

In some ways, the most impressive acting comes from the "troupe," the group of inmates who do not have specific roles in Sade's play, but behave as a sort of raving chorus. Like naughty children, they play leapfrog, poke each other's middles, and pull each other's hair. They pick at their noses and masturbate, they jeer at actors who forget their lines.

The troupe also represents the terrifying mob. They can loll about disinterestedly, and then be seized by frenzied fits. As one patient suddenly bursts out, "Man is a mad animal." He growls and flails his arms and butts the nurses and nuns, yelping, "I'm a thousand years old and I've commited a million murders--prisons don't help, chains don't help...I'm not through yet...I've got plans...."

This is Weiss's key point. Man is a brute and he always will be; his ideological fervor is only inspired by latent lust and violence. As Sade himself quips, "People join revolutions when the adrenaline builds up." The radical soapbox priest, Jacques Roux, is played by a vociferous, apoplectic inmate (Kristen Gasser) who is restrained by a gag. Aroused by Corday's ghoulish description of a beheading she witnessed in Paris, the patients play at guillotining each other, tossing about a large red ball--a dismembered head--and tittering like demons.

At the end of the play, Evrard sees her production turn into a fiasco. When Marat is stabbed, the passions of the inmates erupt. They assault one another, pummel away at the nuns, rush at the bars which separate them from the audience and clamor for freedom. This is how the mob acts when it rises up in revolution. We are all maniacs. Weiss seems to say, and society is our asylum.

This idea of human savagery is further reinforced by Richard Peaslee's songs. Set to lilting tunes resembling those of Kurt Weill's, the words are as bitterly ironic as Brecht's. Throughout Marat/Sade, the singers repeat the refrain: "Marat we're poor/And the poor stay poor,/Give us a rise and we don't care how,/Give us a revolution...now!" The link between mass revolt and sexual lust is the theme of another rollicking song: "And what is the point of a revolution/But general copulation?" On the word "copulation", the singers perform a neatly-choreographed little wind-up dance.

THE INMATES' extravagant lunacy, however, obscures part of Weiss's political message under a barrage of pranks and gibberish. A post-World War II dramatist, he aims his satire of the Reign of Terror at 20th-century political folly. Too often, however, the patients of Charenton drown out Marat's speeches with their rumpus of wild cheers and spiteful taunts.

By the same token, Sade's scandalous love of physical torment overshadows his political convictions. In the famous whipping scene, for example, he strips to the waist and orders his hands bound. Summoning Corday to his side, he provides her with a whip and drawls: "And even now I should like to have this beauty here, who stands there so expectantly, and let her beat me while I talk to you about the revolution." The audience and other inmates gasp in horror and anticipation. Sade proceeds to crumple, groan and writhe on the floor, creating a sensation but garbling every word of his speech.

Although the political ideas are overwhelmed by the tide of general insanity, the play on the whole is gripping and provocative. Simonne Evrard sits in her spectators' box, coolly removed from the raging inmates. In one corner, Marat squats in his tub. In the other, Sade leans casually against a pedestal. The other players in the historical drama form a ring. Behind them are the rest of the patients, sitting on benches beneath X-shaped projections that could be gallows or crucifixes. Beyond the stage sits the audience, who must absorb Weiss's ideas and interpret them. But the actual audience is not that far removed from the madhouse. As the inmates bang at the bars confining them, they practically touch us. Their wretched plight is ours; we are all part of one big batty family.