BOOK REVIEW : Guises of the Deity Through the Ages : A HISTORY OF GOD: The 4,000-Year Quest of Judaism, Christianity and Islam <i> by Karen Armstrong</i> ; Knopf; 427.50, 460 pages

“A God-shaped hole” is how Jean-Paul Sartre described the longing in human consciousness for an all-powerful deity, and Salman Rushdie once observed that he tried to fill the hole with literature. Karen Armstrong, by contrast, fills it with history in her ambitious new book, “A History of God.”

In fact, Armstrong’s book is slightly mistitled--it’s not so much about God himself, but rather the idea of God as it has evolved over the last 5,000 years in art, politics, science and philosophy.

“This will not be a history of the ineffable reality of God itself, which is beyond time and change,” she announces at the outset, “but a history of the way men and women have perceived him from Abraham to the present day.”

So Armstrong neatly sidesteps the ultimate question for which only true believers have an answer: Is there a God?

Although she is a former Roman Catholic nun, Armstrong approaches God as a historian and journalist, not as a theologian. Therefore, the book surveys the startling and sometimes contradictory guises that God has taken in the human mind.

“A History of God” is like a museum where the relics of human faith have been placed on display in glass cases, and Armstrong is our chatty and engaging docent. She shows us the companionable God of Genesis who broke bread with Abraham, the fire-and-brimstone “God of Armies” who thundered atop Mt. Sinai, the God of Christianity who is “the Word made flesh,” the God of Islam who is called by 99 names in the Koran.

“Is the ‘God’ who is rejected by atheists today,” she pointedly asks, “the God of the patriarchs, the God of the prophets, the God of the philosophers, the God of the mystics or the God of the 18th-century deists?”

That’s not to say, however, that Armstrong lacks a point of view on the subject of God. Indeed, herprevailing tone--reasoned, compassionate, erudite, and even magisterial--is sometimes slightly torqued by one of Armstrong’s passions.

For example, Armstrong is especially interested in how women have fared in the history of religion, and she suggests that ancient paganism was more affirming of women than the monotheistic religions that replaced them. Ritual sex as practiced in pagan religions, she suggests, actually embodied the values of “wholeness and harmony” that were purged from Judaism, Christianity and Islam after these faiths were “hijacked” by male clerics.

“Women were marginalized,” she concludes, “and became second-class citizens.”

Armstrong is open-minded toward virtually every mode of faith she has studied, ranging from the Canaanite fertility cults to the “heroic atheism” of Nietzsche, and the book is considerably enriched and enlivened by her cheerful approach to controversies that once sparked crusades and inquisitions.

Still, she seems especially sympathetic toward Islam, which she explains and defends with rather more fervor that she displays toward other religions.

“The intolerance that many people condemn in Islam today does not always spring from a rival vision of God but from quite another source,” she insists. “Muslims are intolerant of injustice, whether this is committed by rulers of their own--like Shah Muhammad Rez Pahlavi of Iran--or by the powerful Western countries.”

Armstrong only briefly ponders the crucial and even ominous question that her book necessarily raises:

“How will the idea of God survive in the years to come?” she muses aloud. “For 4,000 years it has constantly adapted to meet the demands of the present, but in our century, more and more people have found that it no longer works for them, and when religious ideas cease to be effective they fade away.”

Armstrong seems to embrace a spiritual version of natural selection--what survives in religion, she suggests, is what works--and so we may expect that something will take the place of what she calls “the growing blankness where God once existed.”

But, by the time we reach the end of “A History of God,” Armstrong leaves us with some anxiety about exactly what will fill the God-shaped hole in the next millennia.