''I was brought up, like most Englishmen, to respect free trade not only as an economic doctrine which a rational and instructed person could not doubt but almost as a part of the moral law,'' wrote John Maynard Keynes in 1933. And indeed, to this day, nothing gets an economist's blood boiling more quickly than a challenge to the doctrine of free trade.

Yet in that essay of 70 years ago, Keynes himself was beginning to question some of the assumptions supporting free trade. The question today is whether the case for free trade made two centuries ago is undermined by the changes now evident in the modern global economy.

Two recent examples illustrate this concern. Over the next three years, a major New York securities firm plans to replace its team of 800 American software engineers, who each earns about $150,000 per year, with an equally competent team in India earning an average of only $20,000. Second, within five years the number of radiologists in this country is expected to decline significantly because M.R.I. data can be sent over the Internet to Asian radiologists capable of diagnosing the problem at a small fraction of the cost.

These anecdotes suggest a seismic shift in the world economy brought on by three major developments. First, new political stability is allowing capital and technology to flow far more freely around the world. Second, strong educational systems are producing tens of millions of intelligent, motivated workers in the developing world, particularly in India and China, who are as capable as the most highly educated workers in the developed world but available to work at a tiny fraction of the cost. Last, inexpensive, high-bandwidth communications make it feasible for large work forces to be located and effectively managed anywhere.