It’s Not Easy Being Green : An alternate history of the Wicked Witch of the West : WICKED: The Life and Times of the Wicked Witch of the West, <i> By Gregory Maguire (ReganBooks/HarperCollins: $24; 406 pp.)</i>

Gregory Maguire’s “Wicked” reveals the untold history of the Wicked Witch of the West, including her years as the alienated college roommate of a vain, social-climbing beauty named Glinda. All of which sounds deliciously high camp--like a Charles Busch take on the Oz mythos.

But “Wicked’s” subversive strategy is to suck you in with such juicy pleasures and then hit you with the hard stuff. For “Wicked” is ambitious; it sets out to explore the circumstances that create evil (if evil can even be said to exist). That it does so by utilizing a character from children’s literature, rather than a historical figure, is part of its genius. After all, the Witch is as recognizable to us as any historical tyrant, yet we know her only as evil incarnate, a construction-paper villainess. Can we now, as adults, accept a retrofitted history of how an otherwise well-meaning woman went so wrong--to the point of actually sympathizing with her? (And if we can, what unsettling things can we infer about “absolute” evil in our own world?)

Late in the novel, before our pea-green heroine, here named Elphaba, has any idea that she will one day become a witch, she overhears a traveling companion comment tartly on a folk tale. “To the grim poor there need be no pour quoi tale about where evil arises,” the traveler says, “it just arises; it always is. One never learns how the witch became wicked, or whether that was the right choice for her--is it ever the right choice?” By the end of “Wicked,” we’ve seen that it is indeed the right choice for Elphaba, because the particular brand of evil that has defined her for us--hostility to an entrenched authority--is shown to us in a new light. In Maguire’s Oz, the real evil is the totalitarian Wizard and, to a lesser extent, Elphaba’s sister, Nessarose, who is known as the Wicked Witch of the East not because she’s diabolically bad, but because she’s angelically good--she’s horrifically holier-than-thou.

Elphaba, by contrast, is self-effacing, a woman who scorns power and claims not not even to have a soul. We meet her first as the deformed infant daughter of a humorless preacher, Frexspar, who tries to convert Munchkinlanders from “paganism” (they believe in the fairy goddess Lurline) to the worship of the “Unnamed God.” Frexspar sees Elphaba’s green skin as that god’s judgment on his failures--or on his promiscuous wife, who’s so addled from chewing narcotic leaf that she can’t remember exactly who fathered Elphaba. For all she knows, it could have been an elf. (We’re clued in to Elphaba’s real sire later, and it’s a shocker.)

We next see Elphaba at the university, being scorned (at least initially) by the spoiled heiress Glinda, with whom she’s forced to room. But during this period, Elphaba takes up the cause of Animal rights--that’s upper-case A, denoting sentient Animals as opposed to dumb animals. (Think of the cowardly cap-L Lion.) The Animals in Oz are being systematically stripped of all civil rights (in a risky parallel to events in our own century), which ultimately sets Elphaba dead against the Wizard.

Later, after a frightening attempt to recruit her to join the Wizard’s side, Elphaba flees to the Emerald City to join an underground extremist group dedicated to toppling the tyrant and restoring Animals to citizenship. But she’s sidetracked by a love affair with an old college chum, now chieftain of the western province of Vinkus (home of the “Winkies”). When he’s killed by police because of the attachment, Elphaba abandons her politics and travels to his craggy homeland to beg forgiveness from his widow. But the widow, while accepting her as a house guest, refuses to hear her petition. Elphaba, unable to depart without clearing her conscience, remains self-exiled in a tower, becoming increasingly witchlike, until the Wizard’s long arm reaches her--and his appointed assassin, Dorothy, arrives. And we all know what happens then. Or rather, we thought we did.

“Wicked’s” flap copy compares it favorably to both J.R.R. Tolkien and Gabriel Garcia Marquez, and for once that’s not just P.R. lip flap. Maguire fills in L. Frank Baum’s broad outlines to create a fully realized fantasy realm that coheres politically, culturally, sexually--and magically. It’s a staggering feat of wordcraft, made no less so by the fact that its boundaries were set decades ago by somebody else. (I’d imagine that, quite the opposite, that would’ve made it all the more difficult.) I was devoted to the Oz books when I was young, and it’s thrilling to see the familiar places and personages fleshed out with added literary depth. (One small aside: Although Maguire generally remains faithful to Baum’s books, his Witch and Dorothy owe much more to Margaret Hamilton and Judy Garland. The performances of these two actresses in MGM’s 1939 “Wizard of Oz” movie are apparently too indelibly etched in our communal imagination ever to be effaced, even for literary fealty; I know this is true for me.)

Maguire’s larger triumph here is twofold: First, in Elphaba, he has created (recreated? renovated?) one of the great heroines in fantasy literature: a fiery, passionate, unforgettable and ultimately tragic figure. Second, “Wicked” is the best fantasy novel of ideas I’ve read since Mervyn Peake’s “Gormenghast” or Frank Herbert’s “Dune.” And with its Oz connection, it’s almost certain to sell well. Would that all books with this much innate consumer appeal were also this good. And vice versa.