As the ditty has it, "Hinomous, honomis,/ Woman's monogamous. Honomis, hinomous,/ Man is polygamous. It's a wonder that the male of the species ever accepted the concept of marriage, which binds a man so unnaturally to a single woman. There comes a time in the life of every college sophomore coed that she begins to question the wisdom, even the truth of this saying. Given the paucity of monogamous relationships throughout the animal kingdom, is it not possible that the female of the human species has varied tastes as well? This is the conclusion drawn by James Toback in his risky new film, "Two Girls and a Guy," a chancy venture in that its dialogue feels almost completely improvised while its appropriate forum is live theater. Frequently materializing as an actors' exercise designed to showcase the many talents of Robert Downey, Jr., "Two Girls and a Guy" suffers from the claustrophobic ambience of a photographed play and a tendency to repeat and rehash prosaic dialogue. Its particular appeal is in watching Downey, a master, at work, particularly when he seems to be exorcising his own demons, and in appreciating the facial expressions on its three characters who are filmed by Barry Markowitz in bold closeup.

"Two Girls and a Guy" recalls "The Designated Mourner," David Hare and Wallace Shawn's more static photographed play with Mike Nicholas as a flawed individual who, joining a cerebral family that takes pleasure in the arts, just doesn't get it. Downey, in the role of a narcissistic though down-on-his- luck actor, is forced into a dialogue with two young women who discover that the man has been two-timing them, spending three nights per week with one and three nights with the other, though insisting to each that she is his exclusive lover.

A more conventional story would have the girls seeking revenge on the duplicitous performer, who touches our heartstrings each time he shows his concern for his dying mother and tickles our funnybones when backed to the wall by his interrogating girl friends. Toback, who has written the script which he directs almost completely within a spankingly decorated Manhattan loft, takes on a different center. His women want simply to know why their man insists on seeing two different, lovely creatures, and while receiving only a fragmented answer to their query, they wonder why he simply did not tell each of them the truth.

As a date movie, "Two Girls and a Guy" might have the young men in the audience squirming as they recognize some of the lines they traditionally feed their dates. Blake, as the Downey character is known, has relied on hackneyed phrases which had been surprisingly accepted by each woman, expressions such as "I never experienced real love before I met you," and "You own my [sexual member]." Lou (Natasha Gregson Wagner) and Carla (Heather Graham), in turn, respond with "I thought you loved me, I really did," and "He showed how helpless he was in the grips of overwhelming passion."

As the camera pans about the loft--which features lots of space on a bare, polished wooden floor, Japanese curtains separating the bedroom from the living area, a grand piano on which rest a picture of Blake's mother and another of his girl friend du jour--it rests on two provocative scenes which are almost embarrassing in their intensity. In one situation, Blake looks in his bathroom mirror and sheds a tear while intoning, "When are you going to shape up," a line which will have the cognoscenti in the audience wondering whether he is talking about Robert Downey Jr. as much as about Blake. In another, an extended sexual sequence between Carla (Heather Graham) and Blake in the bedroom, we watch the steamy progression filmed in shadowy dimness while the camera frequently pans outside to show Lou sitting just outside, listening to everything without showing signs of envy.

Heather Graham is stunning to look at and provides a foil for the cuter, if less beautiful streetwise Wagner. Downey turns in a forceful and varied performance as foiled lover, Shakespearean actor, and concerned son. On the whole, however, "Two Girls and a Guy" is a work for the stage and could use pruning and a tighter script even at a fairly brief 92 minutes.