By James Conaway

Richard Todd/Houghton Mifflin

529 pp. $24.95

FOR THE average wine drinker, Napa Valley is a magical name, a name to conjure with, a name like Camelot or the Forest of Arden: Is there really such a place, and if so why is it so prestigious, and why does all the best American wine seem to come from there? There is such a place; it's about 50 miles north of San Francisco, stretching from Calistoga on the north to the town of Napa in the south. And for reasons of climate and soil, combined with a concerted human effort going back several generations, the best wine in America, some of the best wine in the world, does come from there. Conaway's Napa explains it all in copious detail, perhaps even too copious; the publisher accurately describes it as an "extravagantly informative book."

Conaway at one time worked as a feature writer at The Washington Post, where his duties included a wine column. He has written five previous books since leaving The Post, including some fiction. It all shows in this book. The research is monumental, the work of an assiduous reporter; Conaway's knowledge of wine and wine-making is formidable, and in places in the book he brings to bear all the talents of a popular novelist. For Conaway the story of Napa Valley is the story of a half-dozen prominent families, including their most private personal dramas. There are unfaithful wives, mistresses, wayward children and deaths by suicide. After the death of former Inglenook owner John Daniel, Conaway gives us the reactions of his daughter Robin in intimate detail. "What followed would always be vivid in Robin's mind, dominated by a desperate sense of loss, the race north to Rutherford, the struggle with her mother, the flood of detail that robbed her of grieving." And so on; there is more. No doubt Conaway did interview Robin Daniel Lail, but he also applies a vivid imagination and the technical skill of a mass-market novelist. Later he gives us an account of a stretch-limo pilgrimage by winery patriarch Robert Mondavi and his entourage to the town near Lodi where Mondavi grew up as a boy. It is full of dialogues and of details that only an angel, or a fly on the wall of the limo, could have known. "First the priest fell asleep, then his companion, then Margrit {Mondavi's wife}. Her head dropped and she listed to one side, the brim of her straw hat bent on the priest's shoulder."

Enclosing these large chunks of pseudo-fiction is the history, which is mainly a history of business and politics. This seems tedious at first, but if you pay attention to it, it becomes fascinating. The Napa Valley contains the most valuable farm land in the world. The wine-making was begun by a few families on the heels of Prohibition. They possessed some excellent vineyards but had only a rudimentary knowledge of how to make cheap wine. The quality of the output was improved by their children, certain wineries began to acquire international prestige, and many of them were sold to conglomerates (among the large companies that bought into the Valley were Heublein, Nestle, Seagram and Coca-Cola). In reaction to this commercialization, "boutique wineries" sprang up, run by San Francisco bohemians, former wine students from the University of California at Davis, and celebrities like the film director Francis Ford Coppola. Other people set up "chain-link wineries," where they grew no grapes at all, but pressed wine from grapes bought from other growers. THE SECOND half of the book is dominated by the Great Arguments, as obsessive and enduring as the Polish Question: the dispute over the setting apart of an agricultural preserve to save the vineyards from the encroachments of development and tourism; the question whether a Wine Train should be built to bring thousands of tourists daily into the Valley, and the "75 percent solution," the controversial principle that at least 75 percent of the grapes that go into Napa Valley wine should be grown in the Napa Valley. To an outsider, it seems astonishing that wine labeled Napa Valley should contain even one grape not grown in the Napa Valley, but this book makes you an expert on these matters, even while it confuses you.

There are over 500 pages of it, and you have to pay close attention. The switching from history to pseudo-fiction and back gain produces a splintered and tesselated structure that puts strains on your short-term memory and requires frequent reference to the index. Gustave Niebaum, the 19th-century founder of Inglenook, wrote, "A business is but the lengthened shadow of a man." This is Conaway's premise too, if you add, "and of his women and his children." As copious and complex as it is, Conaway's story is essentially that of a half-dozen powerful families who dominated the Valley and finally won world-wide acclaim for its products. The climax came at a blind tasting in Paris in 1976, when French experts gave higher scores to Napa wines than to the best French vintages; one taster commented, "the magnificence of France . . . certainly a premier grand cru of Bordeaux" on what was in fact a Napa Valley cabernet. When the results were published, the embarrassed judges had all kinds of alibis: the crowds distracted them, the day was hot, the French wines were disturbed on their journey to the hotel, the wines were presented to them in the wrong order. It was not a great day for the noble tradition of French wine.

There is one slight imbalance here, I think; in attributing the phenomenal success of California wines to the efforts of a few strong figures, Conaway slights the really significant contribution made by the enology and viticulture departments at the University of California at Davis, which set out in the 1960s on a deliberate program to duplicate and then surpass the famous French vintages through the application of exact science and technology. If ever there was an example of the successful advancement of a state industry by a state university, this is it.

MacDonald Harris's most recent novel is "Hemingway's Suitcase." He lives in Southern California.