DIRECT PRODUCTION workers-machinists, bricklayers, farmers-are a steadily declining portion of the work force in a developed economy. The fastest growing group consists of "knowledge workers"-accountants, engineers, social workers, nurses, computer experts of all kinds, teachers, and researchers. And the fastest growing group among knowledge workers themselves are managers. People who are paid for putting knowledge to work rather than using brawn or manual skill are today the largest single group in the American labor force-and the most expensive one.