AT ONE LEVEL, the story of the Durants is a family saga, of the kind we like to consider traditionally American. The hero is born to French-Canadian immigrant parents in 1885.He turns into a brilliant student and is ticketed for the priesthood. But he soon loses his faith and slips into agnosticism, socialism, vegetarianism, free love, and other new-century enticements. He leaves home, and in 1912 is teaching at an anarchist-sponsored progressive school. One of his students is the 14-year-old daughter of Russian-Jewish immigrants. They fall in love. Pygmalion-like he changes her name from Ida to Ariel, pours poetry into her willing ear, woos her strenuously on bicycle and canoe trips. They marry in 1913 - serious young rebels, destined for a life of garrets and communes, perhaps even jails and strikes.

But instead, Will plunges frenetically into making a living. His work involves constant travel. There are long separations, reams of letters, occasional tiffs. She worries that he will philander; he frets over her addiction to Greenwich Village life. But they remain in love. Money comes in; reputation grows. They move to successively better homes, raise and educate two children (one an adopted nephew), take many trips to Europe. The youthful radicalism turns into a regular support of Democratic presidents, and a rueful acceptance of the wild ways of grandchildren in the 1960s. The end is a California old age, with aches and pains assuaged by fame, the friendship of the great, and sunset love.

Pure television. But what makes it all special is Will's "business," which is the popularization of knowledge. Shortly after marriage, he took a doctorate in philosophy at Columbia, but the university classroom was not his future. Already he was known as a first-rate expositor to adult audiences. In 1927 some of his talks and pamphlets were published as The Story of Philosophy , which became a smash best-seller, and made him a star of the lecture circuit. So off he went for 40 years of holding forth at churches and temples and colleges and civic auditoriums and clubrooms, wherever managers could book an audience to learn that learning could be pleasurable. Meanwhile, he began to write a complete history of civilization that would synthesize all those developments usually treated separately and to their loss art, science, literature, politics, economics, religion. WIth Ariel's help, at first simply acknowledged in prefaces, but eventually with co-author credit, he went on with it year after year. The first volume. Our Oriental Heritage, appeared in 1935, and the presumable last one. The Age of Napoleon , in 1976. By then the Durants had won numerous prizes, earned the acclaim and acquaintance of notables and stars the world over, and become a kind of national institution, as signaled by their being awarded the Medal of Freedom at the White House in January, 1977.

But amid all the best-sellerdom, they had also been the targets of criticism by many scholars who insisted that the attempt to handle sixty centuries of human history resulted fatally and inevitably in shallowness and error. The summation of one such reviewer, J.H. Plumb, in 1963, typifies the strongest attacks. Of their Age of Louis XIV he said: "Everything is gloss, smoothed away, made inevitable . . . the rhythm and flow of history . . . reduced to a collection of personalities . . . so facile that the unwary will be first ensnared and then misled."

The Durants' autobiography will probably not convert any readers either to Professor Plumb's point of view or that of the various prize committees who have honored the pair. But it does illustrate both their strengths and weaknesses, and suggests a basic source of their popularity.

The strengths are diligence, intelligence and enthusiasm. There is heroism in Will's struggles to write or proofread year after year in trains, planes and hotel rooms, battling off fatigue and road illnesses with his favorite remedies of fruits, nuts, cold baths and enemas. Ariel records her own years of endless, patient reading and note-taking (as many as 30,000 note-slips consumed per volume) as they rolled on through the centuries. Together they covered enormous distances in visits to the monuments of culture which they wanted to see first-hand, from Angkor Wat and Agra to Delphi and Chartres. Both of them, especially Will, responded to what they read and saw with lovers' undiscriminating passion.

Yet it is exactly that lack of sieving that is a drawback. The autobiography is written by both of them (Ariel dictating her sections to Will for polishing), and is clearly based on an overpowering accumulation of journals, letters and papers prudently squirreled away for years. It has far too many itineraries, dates, prices and trivial tidbits - which is precisely the case with some of their volumes.

Likewise, the writing has that easy and banal quality found in so many fascinating and well-informed talkers. Durant's pen and tongue fly pleasantly along, because he rarely doubts anything he is saying. He is a natural-born compactor and condenser, snapping up the first figures of speech that come to mind. Of the Grand Canyon, for example, he writes that it is full of "rocks carved as if by Brobdingnagian architects - you can hardly believe that they are the work of water wearing away hard stone . . . What a lesson in patience!" Yes, or in the obvious. And Durant explains that John F. Kennedy was killed "by one or more of those many men who live on the threshold of insanity, waiting for the winds of religious or political hatred to topple them over into heedless, head-long crime." How neat. It is unfair, of course, to isolate sentences in this way. But they may explain why writers who know how desperately hard it is to get one fact straight, nail down a single generalization, or fathom another's mind are gored by the Durants' sunny simplicities.

Yet the popularity is undeniable. Why? Part of the answer lies in our "culture" industry, which feeds a traditional American democratic hunger for easy uplift with the intellectual equivalent of TV dinners. But I suspect there is something else.The key is Durant's late 19th-century faith in the simple concepts of history and civilization themselves - defined by him as "social order promoting cultural creation." Despite his stated skepticism about historians who explain the past, what he has told his book club audiences for five decades is that there are patterns and structures, tides and movements in history. Somehow, out of chaos, civilizations emerged, and if one unravelled and went under in a civil war or a barbarian incursion, another painfully emerged elsewhere. Our strange biped species, so prone to savagery, can also produce the restraints of law, the inspiration of faith, the spurs of beauty and nobility. "It is time," he wrote in 1963, "for all good men to come to aid of their party, whose name is civilization." If this sounds like uplift for the booboisie, as H.L. Mencken called the American middle class, be advised that Mencken deeply admired Durant.

People appear to need this assurance that there is a purposeful flow in the life of the whole human race; that their instant of existence matters in an overall scheme: that their saints and rogues are only themselves writ large.

Scholars are not wrong in their specific criticisms of the Durants - too much reliance on second-hand sources for the non-cultural materials, and ignorance of recent academic work. (Their answer is that younger scholars have rarely added anything to the classic accounts of the golden era of historical literature, but in many fields this is simply and flatly wrong.) Yet the quarrel goes deeper. Today's academicians analyze instead of synthesizing. They forgo the comforts of elucidation, find complexities in place of regularities, dissolve old boundaries between periods and categories. But they have therefore retreated from a search that began with the first primitive sacrific to an unknown god - the quest for answers to "Why are we here?" and "What must we do?" When professors fly from questions of duty, reward and justice to models and mathematics, they must expect that a public already deprived of its old faiths, both secular and celestial, will continue to long for more nourishing knowledge. The Durants fill a spiritual vacuum.

This is not to reproach scholars for not creating a new faith, which they cannot do, but rather to call attention to a problem. Something in the way in which we now educate our young mandarins has made many of them insensitive to ordinary yearnings. It is one thing to despise authors who gain popular success, but it can come dangerously close to despising people themselves, an academic attitude that is both unworthy and self-destructive.

But no fair-minded reader will be able to finish this book and seriously dislike the Durants. They are endearingly like many intellectual, ex-bohemiangrandparents - sincere, well-meaning, honestly hurt by criticism, unwilling to say nasty things about their critics, a little naive in their pride, but more mature in knowing life's limits than we sometimes give them credit for. Perhaps the best final words are those written by Garrett Mattingly in 1957. They were about Will, but can stand for them both. Mattingly found that The Reformation did not "represent the state of historical scholarship in the middle of the twentieth century." But, he said:

"Mr. Durant's public will care very little about this, of course, and who is to say that they are wrong? Their favorite author may be nothing of a historical scholar, but he is a capital story-teller, a constantly readable expositor, a widely read and highly cultivated man, essentially kindly and well-meaning. Time spent with such a person cannot be time wasted."