MEN HAVE bigger brains than birds. Somewhere in there, tucked away under the folds of our brains, is a unique sense of purpose; we must exist for a reason, we think. William Wharton's soaring Birdy is about that sense of purpose. Birdy and Al--the novel's heroes--come to realize life is a game worth playing, not merely a block of time to pass away. They force their minds to fly.

A novel that inspires book critics to nothing but rave reviews is a rare bird. Birdy has already been hailed as a modern classic. The Village Voice called Birdy, published in January, the novel of the year. The New York Times used adjectives like "enchanting" and "electrifying."

It behooves the young critic to find fault with Birdy. How can a book about birds be "electrifying?" Yet Wharton has crafted an astonishing novel. Birdy's few faults are light as air. The critic can sing only praise.

Birdy and Al are boyhood chums. They fall out of the nest at the same time, both managing to land on their feet in a poor neighborhood outside Philadelphia. Al is a Sicilian tough guy, dark and intent on making himself a strongman. He excells as an athlete, making it with the cheerleaders, before getting his face and gut shattered by artillery in World War II.

Birdy is skinny--hence the nickname--clever, and eccentric. He learns to live with pigeons, sews himself a pigeon suit, even fashions wings for himself after practicing flapping his arms. He studies canary language, and falls in love with a cute canary named Perta with whom he has his own brood, before finally succumbing completely to bird madness.

The boys have a hero. He is Richard Halliburton, who sent a message from a Chinese junk while crossing the China Sea: "Having a wonderful time, wish you were here instead of me." The emphasis is on escape: escape from parents, school, war, self, and finally, madness. Al learns that he cannot muscle his way through to escape. He must follow Birdy in struggling to wing his way to freedom. Imagination takes them a long way. As Al puts it, Birdy makes up the lying part and I back him with the details to make it seem real. What a team."

We actually see Birdy fly. We believe that he speaks canary language, that he understands the birds' system of time, that he knows what it is like to soar higher than the trees and that Perta, the yellow canary with the green eyebrows, can inspire Birdy to love and wet dreams. We believe he is a bird.

"The first time I flew, it was being alive," he tells us. "Nothing was passing under me. I was living in the fullness of air; air all around me, no holding place to break the air spaces. It's worth everything to be alone in the air, alive."

While we suspend disbelief, we also hold back cynicism. We glide in Bridy's tailwind, tramp behind Al and Birdy through a series of touching, painful and often hilarious boyhood adventures, and we dodge mines and shells with Al as he takes on the Germans. Along the way, Al discovers that his muscle is a front hiding a fearful but honest man-boy. Birdy confronts his birdness and slowly lets it migrate from him.

The boys sing in two-part harmony. Al speaks solidly, narrating the story of their lives step by step, unhesitantly supplying details and background references. Birdy speaks in a more flighty tone, but in sharper focus, offering the history of his bird colony and telling us how, in his dreams, he goes from boy to bird.

WHARTON'S WRITING quietly expresses the ultimate humanity of the two boys. Wharton writes cleanly, simply. His words let Birdy fly. Wharton's writing is fun and inventive. For example, about canaries: "They were put in cages because they sang and now they sing because they're in cages." Or, on feeding birds: "I try to think what it would be like to have some gigantic bird come and stick his claws into the window of my room with some potato chips or a hoagie."

Wharton waxes brilliant when writing about Birdy's dreams. In his dreams, Birdy conquers his fear of being caged by the wire mesh and two-by-four boards of his own aviary. Birdy lives for the night when he can dream. Eventually, life imitates dreams and Birdy gains an easy, prophet-like sense. He even comes to dream within his dreams.

Birdy could serve as a manual for bird watchers and bird breeders. Wharton knows his pigeons and canaries. We learn about feathers and feet, eating and droppings, breeding and dying.

William Wharton is a pseudonym for the wordly, remarkable artist who wrote Birdy. Presumably, he uses a pseudonym to protect his painting career. He is old enough to be a grandfather, but Birdy is his first novel.

"It's too bad people are so old when they get to be grandparents," laments Birdy. If Birdy is Wharton's grandchild, it was worth waiting for. Wharton has taught it to fly as well as any canary could teach its young.

On the surface, Birdy is a crazy novel. But Birdy has a response: "There's no end to the absurd things people will do trying to make life mean something...Maybe crazy people are the ones who see things clear but work out a way to live with it."