Rene Clement's Purple Noon (Plein Soleil) is the highly successful marriage of at least two movies. By turns a mystery thriller and a beautiful portrait of the Mediterranean, it emerges as a poignant statement of human corruption in a modern Eden.

Movie number one is the thriller. A destitute American named Tom has been commissioned to lure an expatriate Phillipe away from Italy and Marge, a beautiful but suspect art student. Hating his sadistic charge and envious of his wealth, Tom murders him, disposes of the body and in a dangerous game of impersonation seeks to substitute himself for his victim.

Movie number two is Clements Portrait of Eden. His cameras follow Phillipe's sloop Marge along the lush Italian coast from Rome to Sicily. From the Mediterranean setting he creates not so much a background as a circumscribed universe which encloses the action in a glass bell of almost suffocating beauty.

Purple Noon studies its characters carefully, and Clement has made full use of a small but uniformly excellent cast. As Phillipe, Maurice Ronet is more than the usual doomed playboy: he creates a memorable picture of selfish animalism. When Marge delays making love to lecture him on art, he explodes, destroys her notes, and roars "Why do you mix Fra Angelico and love?"

Alain Delon, who established his reputation as Rocco in Rocco and His Brothers, turns in an impressive performance as the debonair murderer lusting for "le meilleur." The entire design to murder Phillipe develops unspoken in his eyes, where greed and hatred of a tormentor become obviously irresistible.

Of the three, though, it is Marie Laforet in the complex role of Marge, who is the most striking. Possessing fascinating beauty, she alternates between passion and great delicacy, never losing control of her enigmatic character's many moods.

But this is Clement's movie, and it is his achievement that his two movies maintain unity. In some of the most exciting moments, for example, he weaves a rich musical score around his protagonist as a constant reminder of Eden.

Man, Clement observes, is given the fruits of earth, yet his own nature leads him to renounce them and turns him to violence and despair. Despite some grisly examples, the point is made gently and with resignation in this movie of rare ugliness and rare beauty.