On God: An Uncommon Conversation By Norman Mailer with Michael Lennon Random House 215 pages; $26.95 Norman Mailer, who died on November 10, knew the pitfalls. Even a world-class novelist has a hard time preventing reflections about the nature of God from sounding pious or presumptuous, especially if he's "ignorant of most of the intellections required of a competent theologian." But Mailer was combative. He was frustrated by the "philosophical paradoxes and evasions that good Christians tie themselves up in" - and the false promises of fundamentalists. With no obligation to defend expertise he didn't have, he decided to follow up on Carl Jung's prescription for mental health: Settle on a cosmology that at least makes sense to yourself. In On God, a series of conversations with Michael Lennon, his friend, literary executor and an emeritus professor of English at Wilkes University, Mailer engages age-old questions often asked by adolescents, scoffers and seminary students: Can God be all-powerful and all-good? Who is the author of evil in the world? Do heaven and hell exist? What is the relationship between faith and reason? Rejecting organized religion and atheism, Mailer offers his own unstable blend of existentialism, gnosticism and pantheism. Presented with an uncharacteristic mix of modesty and moxie, his system of beliefs is idiosyncratic, unsystematic and sometimes silly. But at its best On God is devilishly Maileresque: an iconoclastic, probing paean to human freedom that shouts from the rafters: "God needs us as much as we need God." "Improvising outrageously," Mailer posits a good, powerful, but imperfect God, "an artist, not a lawgiver" and an "embattled moralist." Engaged in a struggle to improve His creation, God's "plan" is a work-in-progress. His fate depends on our actions and the machinations of the devil. God insists on being glorified and needs to be loved, Mailer guesses, because He "has an ego to protect." Unable to be everywhere at once, He is often extenuated, despairing and confused. Mailer's treatment of the theory of "intelligent design" is emblematic of his contrarian, self-contradictory methodology, served up to sustain his convictions about contingency. By trial and error, he writes, evolution could not have produced nature's beautiful forms: "orchids, snowflakes, panthers." The world is "God's major opus." Without Him, "we are back to monkeys writing Hamlet." But Mailer is not an ally of the fundamentalists. He insists that God "makes mistakes." Dinosaurs, he speculates, may have been part of God's plan, "pure and untested" - until he discovered he had "mis-designed them. Back to the drawing board." More heretically, Mailer doubts that the crucifixion and resurrection of Christ were planned in advance. When "the devil won - and Jesus was tortured," God improvised, brilliantly, with the explanation "that His son actually died for our sins." Next time, Mailer warns, we may not be so fortunate. Malevolent design may bring the world to a "rendezvous with extinction." Like so many Jews of his generation, Mailer traces his belief in a limited God to the horrors of the Holocaust. Along with Stalin's gulags and nuclear bombs, Nazi atrocities provided proof positive that God could not be all-powerful and all-good. The Holocaust, he writes, mordantly, "deadened God's wit. Too much was happening at once. God, I will repeat once more, is not inexhaustible." Mailer's faith in God's compassion, he acknowledges, "is arbitrary," shaped less by dogma - or evidence drawn from the world - than by images of his mother lighting the candles and praying every Friday night. God's greatest gift to humanity, Mailer insists, is free will. If goodness was guaranteed to triumph, life would be "an ugly farce, considering how we suffer in the course of the contest." But he's not all that clear about how much freedom we have - and how we might best exercise it. Human beings, he indicates, are "lively but skewed parts of God's vision." We are "tainted, warped, even treacherous in relation to the divine projects offered to us." And the devil "is also present," armed with technology (and plastic, "the perfect weapon" to desensitize human beings). With these external forces, stronger than we are, pushing and pulling at us, how responsible are we for our actions? Mailer asserts that humans "are equals as players to God and the devil," but he doesn't always seem so sure. The best ethical advice he can offer is an injunction that men and women "have the honor to live with confusion" - and the conventional admonition (elsewhere dismissed as a cop-out) that "there is a purpose to it all, that it is not absurd," and that "God needs us." Since "nothing is absolute," ethics mostly involves "sensitivity to the moment" and the will "to reduce ugliness in the world - by a little." The reward, Mailer maintains, is reincarnation. God, the artist, is always looking to do better, and may bring us back, in slightly more advantageous circumstances. Mailer offers no "immediate solace" for our fears, "only an appeal to human pride." He feels no imperative to convert people "right away" because he's "just centered enough" to understand the enormity of the task. After all, it's terrifying to contemplate a world "as open and undecipherable, as chaotic, as wayward, as playful, as perverse, as unexpected, as, in secret, we fear it is." But, thank God, Mailer remains an unrepentant, existentialist missionary, voting for a creator who does not demand "unwavering faith," preferring instead to join hands "and lead us into the unforeseeable future out there with its galaxies, its light years, its enigmas and ultimately, let us hope, its availability." The writer is the Thomas and Dorothy Litwin Professor of American Studies at Cornell University.