”The World According to Garp,” is a gentle, intelligent film and an interesting one.

George Roy Hill has directed ”Garp” very capably, and Steve Tesich’s screenplay is generally sensitive and economical. Together they have done their best to make the novel’s concerns understandable. Though their ”Garp” isn’t wholly successful, their accomplishment in adapting it to the screen as adroitly as they have is impressive. Like the best film adaptations, ”Garp” is essentially faithful to the novel on which it is based, even when it isn’t following the book literally.

Beginning with an inspired title sequence of a baby Garp appearing to bounce in the sky, to the tune of the Beatles’ ”When I’m 64,” the movie traces the entire life of its idiosyncratic hero. He is seen as a boy (played by James McCall) living at the prep school where his mother (Glenn Close) is a nurse, as a teen-ager (played from this point on by Robin Williams) courting the prim girl (Mary Beth Hurt) he will eventually marry, as an aspiring writer, as a successful one and as a devoted father who likes nothing better than to peer at his children when they are sleeping. Finally, he is seen as a man who must endure the coming-to-pass of all the dark premonitions that have ever plagued him. Though its characters boldly declare that life is an adventure and should be lived as one, there is little in ”Garp” to bear out their optimism. The last half-hour of the film is almost unrelievedly sad.

But the early portions, those depicting Garp as a young man, are filled with hope. Garp’s artistic side, described so overbearingly in the novel, is presented sweetly and playfully; there’s an animated segment of crayon drawings as the child Garp tries to imagine what became of his father and a later fantasy sequence showing how Garp the writer might make up a short story. Mr. Hill abandons this tack after a while, but he might well have sustained it throughout the film, because it helps make Garp’s much-praised talent seem believable.

One of the film’s strengths is its graceful way of bringing some of Mr. Irving’s most farfetched inventions to life, among them Garp’s fiercely feminist mother and the Ellen Jamesians, who are more or less her disciples. The Ellen Jamesians are feminist extremists who have cut out their tongues to protest the rape of a girl, even though the girl – now grown up to be Amanda Plummer, who is quite striking in her brief cameo appearance – wishes they would stop. The novel hedges about inventions like the Ellen Jamesians, as well it might; Mr. Irving appears to be ridiculing and embracing feminism simultaneously. Until the final scenes, the movie wisely minimizes their importance and makes them much, much easier to take.

Mr. Williams is at his most affecting with the children; he makes a fond, playful father, a man perfectly at home in a suit of makebelieve armor made of welcome mats and garbage-can lids. Mr. Williams’s role is a very demanding one, calling on him to age from a teen-ager to a family man, a process he has trouble with. His performance is engaging but erratic, more effective in the clownier, busier scenes than in those that ask him to recite lines or stand still. Mr. Williams is much less compelling at rest than he is when free to represent Garp through action. When the role doesn’t call for movement of some kind, he falters.

The rest of the film is expertly cast. Glenn Close, John Lithgow and Miss Hurt are excellent, and so is Swoosie Kurtz in a brief role as a tough prostitute radicalized by Garp’s mother. As for Miss Close, she performs miracles with the toughest of the story’s many difficult roles. Garp’s mother, an entertaining but largely unbelievable caricature in the novel, becomes a full-blooded woman here without losing one bit of her crazy conviction.