Playing today and tomorrow at the Biograph, "The Mission" is a deft psychological thriller embroidered with irony, a look at the wages of purity in a corrupt world.

The mission is an assassination, assigned to a former Iranian Army marksman, Moslemi (Houshang Touzie), now committed to Khomeini; the target is a former Savak colonel (Parviz Sayyad), vaguely accused of torture and embezzlement, who emigrated to the United States after the revolution. In the New York subway, a couple of street punks get to the colonel before Moslemi can; willy-nilly, the stalker rescues his prey, and the colonel, bubbling with gratitude, insists they become friends.

What follows is an interior comedy, akin to "The Misanthrope," as Moslemi, glowering behind his sunglasses and heavy mustache, broiling in his zealotry, sits amidst the effusive colonel, his squeaky coquette of a sister-in-law (Soraya Shayesteh) and his lively children as they virtually force-feed him with delectable stews, entertain him by the piano and drag him off to Coney Island. What's most endearing about this family is the naivete': the colonel's obliviousness to Moslemi's mission as the assassin openly espouses Khomeini, asks suspicious questions, orders him to a deserted roadside -- even when he pulls a gun.

There's a crudeness in the shooting and editing of "The Mission" that bespeaks a small budget, but director Sayyad is shrewd in the way he uses the comings and goings of mass transit to create a lulling rhythmic counterpoint, shrewder still in the orchestration of emotion. The movie has its longueurs, but even the windy debate between Moslemi and the sister-in-law over the virtues of Khomeiniism -- they carry on like Major Barbara and Undershaft -- has its power, since it's so vividly rooted in Moslemi's struggle for honor.

And just when the debate threatens to become onerous, Sayyad himself, as the colonel, dilutes it with his vivacity, his gesticulating hands whipping like the wings of a pinwheel. I've never heard anyone so relish his own laughter -- he seems to smack his lips after each "Ha!"

The Mission, today and tomorrow at the Biograph, is unrated but contains no offensive material.