Pick of the paperbacks; Three Farms, by Mark Kramer. New York: Bantam Books. $3.75.

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

There's a lot in this book, too for readers who don't care much about change and choices on the farm scene.

With a keen eye for detail and a knack for good yarnspinning Kramer brings to life the three farms of the title: a tidy, compact plot in New England, an Iowa spread, and a vast fru it and vegetable oasis in California's desert.