Who's been tampering with the tomatoes; Three Farms, by Mark Kramer. Boston: Atlantic-Little, Brown & Co. $12.95.

If those tomatoes at the supermarket seem paler, thicker-skinned, and less tasty than they used to, you can blame it on progress. The tomato has been selectively crossbred to toughen it for the sake of mechanical harvesting -- a change that slipped past while most of us weren't looking.

Is it too late to prevent more unpleasant surprises in the grocery bag?

Maybe. Maybe not.

In "Three Farms? Mark Kramer sounds a warning: The ongoing agricultural revolution is a mixed blessing. We hardly know yet what we stand to lose and gain by increased automation, fewer family farms, and the concentration of more acreage and influence in the hands of a few agribusiness giants, he says. If we did we might wish it otherwise.

But there's a lot in this book, too, for readers who don't care much about change and choices on the farm scene. Kramer tells a story that's rich as river-bottom land, and tells it masterfully.

He spices his saga of how food gets from field to table with plenty of condiments, including accounts of: what bamboo flowers have to do with the talent of hogs and hens for turning feed to meat; why dairymen call cows "boss"; where Squanto really learned to use fish as a fertilizer (myth notwithstanding); why the cash value of "women's work" fell far short of "men's work" after the Civil War; where one finds the Cleopatra of cows, the most prolific milkmaker in history.

With a keen eye for detail and a knack for good yarn-spinning Kramer brings to life the three farms of the title: a tidy, compact plot in New England, a fertile Iowa spread, and a vast fruit and vegetable oasis in the California desert. And like ghosts in the bedroom of Ebenezer Scrooge, he conjures up farming- past, present, and future.

First we meet Leland Totman, a successful dairyman who still works the rolling Massachussets land his great-grandfather cleared. The embodiment of Yankee ingenuity, prudence, self-discipline, and busyness, he has managed to hang onto his independence despite the pressures to mechanize, increase his herd , and work more efficiently. Such demands have reduced family farms like Totman's to one-sixth the number operating in Massachusetts on the eve of World War II.

Totman has survived as his own master, independent of the banks and corporations, but, Kramer laments, he is also obsolescent in an era when farm work is fast becoming fully industrialized.

"Loss of craft in farming is serious, not just to farmers, but to the nation, " Kramer cautions. "It is the step before loss of pride, loss of personal ethics in trade, loss of stewardship of the land, loss of concern for quality of product. . . . It is part of a grander loss yet, the dying of a system of people making money doing things well."

If Totman is an anachronism in overalls, Joe Weisshaar is a man rooted firmly in the present.

Ambitious, hardworking, savvy, this Iowa hog farmer is nonetheless uncertain that his best efforts will prosper. Weisshaar is far from independent. Because of heavy investment in specialized equipment, he is more securely locked into raising pigs than his father would have been. He eats breakfast standing up and hustles double time to the hog barn, driven by the necessity of meeting monthly payments to the banks that finance his costly business.

He rents part of the 500 acres he works (as do most of the farmers in his state), and he buys (rather than breeds) his animals from suppliers -- which is coming more and more to mean conglomerates. He's worried that hog farming will go the way of broiler chickens, with agribusiness shouldering in at every level, turning the farmers it employs into assembly-line cogs.

For an eerie glimpse of the future Weisshaar dreads, Kramer takes us to a 21, 000-acre California farm. The Corporation and The Machine are in charge here, and the farmer is nowhere in sight.

We arrive after dark. In the glare of headlights and searchlights, trucks, harvesters, tractors, and trailers are congregating beside a 766-acre tomato field. The crop, genetically redesigned to withstand machine handling at the cost of flavor, has been fogged by aircraft spraying ethylene (a natural substance duplicated in the lab) to hasten reddening by a week or more.

As diesel fumes fill the night, 100 laborers climb aboard the harvesters (without the machines 600 would be needed). The vehicles tear into the gray-green plants, stripping away stems and foliage ad dumping tomatoes onto conveyor belts, where human hands frantically sort out green, rotted, or damaged specimens.

For all its promise of mechanical efficiency, Kramer sees a number of flaws in this brave new agricultural world -- stress, waste,likelihook of mismanagement, loss of variety, lack of regard for land and resources. Most of all he sees the demise of pure competition at the level of the farmer, the last bastion of fierce competitiveness in the increasingly integrated food processing chain.

Is such change inevitable? Government policy, technology, and profitability make it seem likely. But if shoppers insisted on tasty tomatoes, who knows? Consumers sometimes make a difference.