NATURE'S GOD: The Heretical Origins of the American Republic. By Matthew Stewart. Norton 448 pages. $28.95.

That the Founding Fathers couched most of their public writings in theological terms acceptable to the masses has led many to believe that the United States was established as a Christian nation. But these proclamations should not deceive the careful modern reader, just as the actual convictions of these men did not escape outraged orthodox theologians of the Revolutionary period.

Although their personal belief systems defy easy labels, as a group the founders were Deists, intellectual heirs to the 17th-century philosophers John Locke and Benedict de Spinzoa. Thomas Jefferson, Benjamin Franklin, Thomas Paine and their fellows were products of the Enlightenment, not the Reformation. And in their correspondence with each other, the founders, frequently attacked as "infidels" and "atheists" in their day, made no bones about what they privately held to be true.

Reclaiming the contributions to radical American thought by these men, together with those of such earlier Revolutionary figures as Ethan Allen and, especially, the little-known Thomas Young, author and philosopher Matthew Stewart finds their evolutionary origins in the work of the great Greek philosopher Epicurus, while offering a bracing antidote to the muddled simplicities and "uncomprehending gaze" of the "common religious consciousness."

Stewart's book is a thorough, persuasive chronicle of the ideas and events leading up to the signing of the Declaration of Independence, as well as an eye-opening survey of some 18th-century Americans whose agitations make the founders look like latecomers to the party.

"Nature's God" is also a lucid survey of radical philosophical thought on the nature of humanity and the cosmos, principles grounded in reason and transmitted from Epicurus via the poet Lucretius, further developed by Locke and Spinoza, and embraced by the Founding Fathers, especially Jefferson.

Often misunderstood, philosophical Deism (as opposed to popular Deism) championed the infinite and eternal (but explicable) universe over the otherworldly spiritualism of Christianity and other faiths. Stewart examines the provocative staple of popular Deistic thought: that nature is God's revelation and that, ergo, God is nature. He then shows Deism is more involved - and more sophisticated - than this interpretation.

On the surface, the founders may have seemed Newtonian or Stoic in their view of the world, but scratch the surface and one finds Locke and Spinoza. "For Jefferson and his fellow Revolutionary Deists," says Stewart, "in the infinite universe of Nature's God, 'creation' and 'Creator' refer to the same thing.

"Spinoza is the principle architect of the radical political philosophy that achieves its ultimate expression in the American republic," writes Stewart. And Locke, far more subversive than he appears, is its acceptable, seemingly pious face. They are two sides of a single body of thought informed by philosophy's "guiding principle," itself an extension of a key insight of Epicurean ideas: that the laws of nature must themselves be lawful, not capricious.

Stewart's probing intelligence and his ability to render undiluted the complex deliberations of these thinkers, is most impressive, though the sheer detail and intricacy of the subject can slip into esoterica from time to time. Yet for the most part, he is admirably clear, the breadth of his erudition and powers of understanding of a high order indeed. The author reads more deeply and perceptively into texts than writers of lesser ability, extracting more than is customary of irony, cloaked meanings and intellectual connections. Stewart, a 1985 graduate of Princeton University whose previous works include "The Management Myth," "The Courtier and the Heretic" and "Monturiol's Dream," also fires many a broadside at the "potted histories of philosophy that fill today's bookstores."

Of his many achievements in the book is the restoration of the reputation of Epicurus. Far from the hedonism with which he is mistakenly associated, and which diminishes a far more comprehensive body of thought, it is Epicurus' concept of a life of virtue and inquiry - a life well lived - that is the source of Jefferson's "pursuit of happiness," not our superficial modern reading of the phrase.

Stewart also makes the circumlocutions of Locke, the complexities of Spinoza and the work of other philosophers accessible to the layperson - no mean feat. But of greatest importance to our understanding of actual history - not romantic illusion or national myth - is how he locates their powerful ideas in the heterodox, Deist origins of the Republic.

To Deists, it was not the existence of God that was in question, but the nature of God. Spinoza believed that God and nature are two ways of talking about the same thing: Nature is God's revelation, and science is its true theology. Genuine piety, he argued, "consists of the scientific study of nature," not blind adherence to sectarian faith. Nature's God, says Stewart, is the presiding deity of the American Revolution. And the Declaration of Independence reflects this, harboring "no appeal to truth handed down from scriptures or announced by prophets." The revolutionary force in the Declaration is the guiding principle of philosophy, which tells us that the universe is ruled by rational laws, and that there are no forbidden questions or sacred truths.

The very least Stewart accomplishes in this book is to eviscerate the "Christian nation" idea. On a broader canvas, the author gives the "common religious consciousness" and much alleged wisdom a fair hearing, then demolishes it utterly, though not without respecting what is humane and useful in faith. More, he provides a multitude of evidence to show how our contemporary religious landscape in the United States is largely a Deist one, despite protestations to the contrary.

Stewart's focus is on the transformational power of ideas, on corporeal reality, not spiritual mysteries. For it is ideas that "make actors out of human beings," he writes, insofar as they inhabit "an open, uncontrollable and inherently unlimited universe of explanation," not calcified dogmas.

"Nature's God" offers a fresh perspective on the complicated, fractious, exhilarating birth of this country, revealing that the often superficially understood words of the Declaration of Independence are even more profound than they seem, for they crystallize a system of radical concepts - a triumph of reason over revelation - that would help decide the course of the modern world.

Ultimately, the enduring question about the struggle for American independence, says Stewart, is not why it happened, but why it was so revolutionary, and why it remains so.

"How the uncommon ideas of radical philosophy came to structure, and then continually restructure, the common experience of humanity is the real story of the American Revolution and of the modern world that emerged in its wake."

Stewart presents this story in all its many facets, compelling us to look at our shared history anew.

Reviewer Bill Thompson is a freelance writer and editor based in Charleston.