Here is how British literary critic Terry Eagleton begins his brisk, funny and challenging new book: "Religion has wrought untold misery in human affairs. For the most part, it has been a squalid tale of bigotry, superstition, wishful thinking, and oppressive ideology." That's quite a start, especially when you consider that the point of Eagleton's "Reason, Faith, and Revolution: Reflections on the God Debate" -- adapted from a series of lectures he delivered at Yale in April 2008 -- is to defend the theory and practice of religion against its most ardent contemporary critics.

But Eagleton, a professor of English literature and cultural theory who divides his time between the University of Lancaster and the National University of Ireland, is determined not to commit the same elementary errors he ascribes to such foes as biologist Richard Dawkins and political journalist Christopher Hitchens. (Those two, collectively dubbed "Ditchkins" by Eagleton, are the self-appointed leaders of public atheism and the authors of bestselling books on the subject, Dawkins' "The God Delusion" and Hitchens' "God Is Not Great.") Atheists of the Ditchkins persuasion have raised valid points about the sordid social and political history of religion, with which Eagleton largely agrees. Yet their arguments are fatally undermined by their own unacknowledged dogmas and doctrines, he goes on to say, and they completely fail to understand Christian faith (or any other kind) except in its stupidest and most literal-minded form.

A few years ago, I read an article by a Roman Catholic theologian who wryly observed that the quality of Western atheism had gone steadily downhill since Nietzsche. Eagleton heartily concurs. He freely admits that what Christian doctrine teaches about the universe and the fate of man may not be true, or even plausible. But as he then puts it, "Critics of the most enduring form of popular culture in human history have a moral obligation to confront that case at its most persuasive, rather than grabbing themselves a victory on the cheap by savaging it as so much garbage and gobbledygook."

Atheists like Dawkins and Hitchens, Eagleton insists, are playing to the high-minded liberal-humanist prejudices of their elite audience and, in the process, are displaying a shocking ignorance of their supposed subject, one that would be deemed unacceptable in almost any other intellectual forum. Would anyone be permitted to write a book about courtly love in the Middle Ages based on several visits to a Renaissance Faire, or a book about Nazism based on episodes of "Hogan's Heroes"?

Yet the argument of "Reason, Faith, and Revolution" goes much further, and is much more complicated, than simply pointing out that St. Augustine and Thomas Aquinas would roll their eyes in disbelief at the third-rate challenge to their God posed by the likes of Ditchkins. Like Lewis Carroll's White Queen, Eagleton is striving to believe several impossible things -- or at least remarkably unfashionable things -- before breakfast. He seeks to reclaim the transformative and even revolutionary potential of Christian faith, in the face of both liberal atheism and right-wing fundamentalism. And as perhaps the most prominent academic Marxist still in captivity, he puts his own faith in the possibility that socialism can survive its spectacular 20th-century self-immolation.

It's only a slight simplification to say that in this compact little tome, which runs less than 200 pages and is largely conversational in tone, Eagleton hopes to save Christianity from the Christians and Marxism from the Marxists. Yet the book's easy-breezy, wisecracking character is deceptive; I had to read it through twice before concluding that it's one of the most fascinating, most original and prickliest works of philosophy to emerge from the post-9/11 era.

I'm not sure there's a human being on earth, Terry Eagleton's family members included, who will agree with everything in "Reason, Faith, and Revolution" -- Eagleton seems delighted with the idea that he will outrage both the secular left and the religious right -- but it repeatedly challenges us to reconsider terms and ideas most of us take for granted most of the time. Is the apparent opposition between faith and reason inherent, or an ideological artifact? How is Western capitalism, agnostic and relativistic down to its roots, to confront a "full-blooded 'metaphysical' foe" (Islamic fundamentalism) that has no problem believing in absolute truth? Whether or not you like his answers, Eagleton approaches all such questions with an open and questioning mind.

As Eagleton ultimately admits, the discount-store atheism of Dawkins and Hitchens is something of a useful straw man, and his real differences with them are, in the main, not theological but political. Still, attacking them in broad and often hilarious strokes -- he depicts Dawkins as a tweedy, cloistered Oxford don sneering at the credulous nature of the common people, and Hitchens as a bootlicking neocon propagandist and secular jihadist -- lends his book considerable entertainment value. More importantly, it also allows him to develop an extended interpretive summary of what he describes as mainstream Christian doctrine, a subject about which (as he repeatedly reminds us) the Ditchkins duo, along with the Western intellectual elite in general, knows almost nothing.

Eagleton's terminology is deliberately provocative, and some Christians won't find his account of their beliefs, colored as it clearly is by the Catholic "liberation theology" of his youth, to be mainstream at all. Still, he is incontestably correct about two things: There is a long Judeo-Christian theological tradition that bears no resemblance to the caricature of religious faith found in Ditchkins, and atheists tend to take the most degraded and superstitious forms of religion as representative. It's a little like judging the entire institution of heterosexual marriage on the basis of Eliot Spitzer's conduct as a husband.

Many secular intellectuals, for instance, have claimed as Christian doctrine "the idea that God is some kind of superentity outside the universe, that he created the world rather as a carpenter might create a stool; that faith in this God means above all subscribing to the proposition that he exists; that there is a real me inside me called the soul, which a wrathful God may consign to hell if I am not egregiously well-behaved; that our utter dependency on this deity is what stops us thinking and acting for ourselves; that this God cares deeply about whether we are sinful or not, because if we are then he demands to be placated."

As Eagleton knows, some Christian believers, especially in the various strains of fundamentalism, would subscribe to most if not all of those propositions. But he's right that from the perspective of the past several centuries' worth of mainline Protestant and Catholic theology, none of those statements is true. In those terms, they range from crude distortions to outright idolatry. Aquinas would tell you that God is not an entity of any classifiable or verifiable kind and most certainly is not a mega-manufacturer who plotted out the universe on some celestial computer screen. Rather, "God is what sustains all things in being by his love, and ... is the reason why there is something instead of nothing, the condition of possibility of any entity whatsoever."

Biologist Stephen Jay Gould's famous pronouncement that science and religion were "non-overlapping Magisteria" has sometimes been viewed as a cop-out, or as a polite attempt to say that the former is real and the latter imaginary. Whatever Gould's intentions, Eagleton agrees wholeheartedly, and finds this view entirely consonant with Christian theology. Dawkins is making an error of category, he says, in seeing Christian belief as a counter-scientific theory about the creation of the universe. That's like saying that novels are botched and hopelessly unscientific works of sociology, so there's no point in reading Proust.

Christian theology cannot explain the workings of the universe and was never meant to, Eagleton says. Aquinas, like most religious thinkers that came after him, was happy to encompass all sorts of theories about the creation, including the possibility that the universe was infinite and had always existed. Indeed, Aquinas would concur with Dawkins' view that religious faith is irrelevant to scientific inquiry. But there are questions science cannot properly ask, let alone answer, questions about "why there is anything in the first place, or why what we do have is actually intelligible to us." That is where theology begins.

Eagleton further argues that not only is the Ditchkinsian version of traditional Judeo-Christian belief a travesty, in which God is envisioned as an unproven and improbable creature like the yeti or the Loch Ness monster, but that this strain of post-Enlightenment atheism cannot comprehend the character of religious faith at all. The creedal declaration "I believe in God" is a statement of action and will; it is performative rather than assertive. It is not equivalent to the claim that God exists (although Christians believe that too). It possesses the kind of certainty that belongs to such wistful sentences as "I love you" or "I believe the Mets are the best team in baseball." It clearly lacks the empirical certainty of the sentence "I believe this maple tree will turn red in October."

Among the many extraordinary positions Eagleton takes in this book, perhaps nothing is more startling than the highly original claim that the United States of America is not religious enough. All right, I am paraphrasing -- what he actually says is that our nation's nauseating, wall-to-wall public piety is strictly pro forma. It's a kind of ideological window dressing for a social and economic system based on the ruthless exploitation of human beings and natural resources, which is about as far from the teachings of that radical Jewish carpenter from Nazareth as you can possibly get.

In one of Eagleton's most ingenious turns of phrase, he describes contemporary Christian fundamentalists as faithless, because they specifically lack the kind of performative faith mentioned above. Philosopher Slavoj Zizek has described fundamentalism as a species of neurosis, in which a person keeps demanding proof that he is loved and never finds it sufficient. In trying to shoehorn anti-scientific hokum into schoolbooks, or wasting money and time on a "creationist science" that strives to prove that the Grand Canyon is less than 6,000 years old and that Noah, for reasons unknown, kicked T. rex off the ark, fundamentalists have become the mirror image of atheists. Unsatisfied with the transcendent and unknowable nature of the Almighty, they've stuffed and jammed him into a dinosaur diorama.

Much of the anti-religious fervor of the Ditchkins school, Eagleton says, derives from a high-Victorian idealism, in which humankind rides the upward-bound escalator of progress and civilization, held back only by the forces of unreason and irrationality. Its adherents see an absolute dichotomy between faith and reason, one that lacks any rigorous philosophical underpinning or an understanding of the inescapable relationship between the two. Heidegger, Wittgenstein and Fichte have all observed in different ways that unspoken assumptions about the world around us (that is, faith) are the precondition of all knowledge in the first place. As for the Enlightenment narrative of steady upward progress from superstition to reason, Eagleton is certainly not arguing that the first is superior to the second. He is suggesting, rather, that the escalator can go up and down at the same time.

What the rationalist myth sees in the modern age are the tremendous advances made in curing disease and in increasing agricultural yield, which neither believer nor atheist wants to do without. It views Zyklon-B and the hydrogen bomb as momentary setbacks, if it notices them at all, and it generally avoids comment about the contradictory and confused economic system our allegedly liberal-humanist age has produced. It's a system, as Eagleton sees it, that pretends to be entirely logical but produces a cruel and irrational result: the poor made poorer and the rich much richer. And what are the greenhouse effect and the melting of the glaciers, if not artifacts of the Enlightenment?

In fairness, neither Dawkins nor Hitchens has been silent about social and environmental questions, and neither they nor their liberal-humanist-atheist peers are directly to blame for the excesses of capitalism. But where they see an uplifting tale of a self-aware species ascending from the swamp of history into the Apollonian light of reason, throwing off the chains of superstition, Eagleton sees a tragic tale of overweening idealism, of men so blinded by their own arrogance that they're eager to throw away lessons taught long ago, by Aeschylus and Spinoza and William Blake and, yes, by Jesus Christ.

You can almost hear the steel chairs creaking as the last secular liberals rise to depart when Eagleton declares where his true disagreement with Richard Dawkins lies, which does not directly concern the existence of God or the role of science. "The difference between Ditchkins and radicals like myself," he writes, "hinges on whether it is true that the ultimate signifier of the human condition is the tortured and murdered body of a political criminal, and what the implications of this are for living."

Eagleton is cagey about the nature of his personal belief. On one hand, he says that he speaks on behalf of his Irish Catholic forebears, "against the charge that the creed to which they dedicated their lives is worthless and void." On the other hand, he never makes any unambiguous truth claims for Christian doctrine, and he remarks that Marx and Nietzsche, unlike Ditchkins, are atheistic in "by and large the right kinds of ways." As he must realize, he is running the risk here of being dismissed as an apologist for not just one discredited faith but two different and nominally opposed ones.

Eagleton believes in Jesus -- believes, that is, in the profound symbolic potency of Jesus -- whether or not he believes that Jesus was the begotten son of God. It's a truism to say that contemporary Christianity has little to do with its eponymous founder, but Eagleton breathes new life into it. He describes Jesus as a Jewish "lifestyle revolutionary" who urged his followers to love their enemies, give away their possessions, and leave their dead unburied, who expressed his love and solidarity for whores, criminals and other "shit of the earth" (the phrase is Paul's), and was tortured and killed for it.

Such a figure, Eagleton suggests, represents "the truth of history," and those who deny it "are likely to adopt some bright-eyed superstition such as the dream of untrammeled human progress," a naive Enlightenment ideal expressed in our time by the likes of Ditchkins. I'm sure Eagleton would be delighted to imagine a resurgent 21st-century combination of democratic Marxism and left-wing Christianity, but he wishes to appear hard-headed and never quite comes out and says that such a thing might be possible. (One could argue that precisely that combination, which was never quite extinguished in Latin America, has made an unexpected comeback in the last few years.)

Having banished such embarrassing metaphysical matters as God and love to the private sector, and having put its faith in an economic system that seems much less eternal than it used to, Western civilization finds itself in quite a pickle. As Eagleton sees it, late-capitalist society believes in nothing except a limited marketplace vision of tolerance, which has spawned a surfeit of irrational belief systems, from fundamentalism to neoconservative imperialism to do-it-yourself New Age spirituality. He even agrees with the neocons and fundamentalists that we cannot successfully combat Islamist zealotry without any core beliefs of our own.

But the cures proposed by the fundies and neocons are worse than the disease, Eagleton makes clear, while the childish and arrogant idealism of the Ditchkins crowd bears no relationship to human history or contemporary social reality. He sees the potential for hope in a "tragic humanism," one informed by the likes of John Milton and Karl Marx but not necessarily religious or socialist in character, one that "shares liberal humanism's vision of the free flourishing of humanity," but believes "that this is possible only by confronting the very worst." We were sent a man who preached a message of love and we killed him; we were given a beautiful blue-green planet to live on and we killed it. What do we do now?