''Banking on the Poor'' is a close examination of a particular few years in the history of the World Bank. The International Bank for Reconstruction and Development (its official name) was born at the Bretton Woods conference in 1944 and for years pursued, in relative freedom from controversy, its dual functions of reconstructing the postwar world and aiding the development of less-developed countries. What interests Robert L. Ayres, a senior fellow at the Overseas Development Council, is how the bank changed after Robert S. McNamara, former secretary of defense, a former ''whiz kid'' at the Ford Motor Company, took over as president in 1968.
To the politically naive observer, the changes put into force by McNamara might seem unexceptionable. In fact many considered them far from it. What McNamara did was shift the bank's aim toward the fight against world poverty. Until that change, announced in a speech in Nairobi in 1973, the bank had pursued its mission of development mainly by financing projects that would augment developing countries' infrastructures - roads, dams, ports, steel mills. These were apparently the best ways to accelerate the economic growth of these countries, and this was presumed to be in the best interests of everyone, including the poor.
McNamara's changes presumed that the best way to help the poor was to redirect bank financing toward them. As a result, the bank began shifting its loan portfolio, first toward projects in poor rural areas; McNamara had first been interested in the small farms of the world and set a goal of increasing their output 5 percent annually by 1980. In 1975 he announced similar efforts on behalf of the urban poor.
What bothered many people in the United States, especially conservatives, about all this is that the US is the World Bank's largest source of funds, and with these changes the bank is doing America less good than ever. The bank's poverty-oriented loans are characterized as ''giveaways'' with low rates of return at best; some are said to support socialistic trends in developing countries, some to aid countries Americans would rather not aid. As a result, the Reagan administration is reconsidering this country's participation in the bank. Meanwhile, the radical left isn't keen on the World Bank either. Its argument holds that the bank's loans all tend to support an existing capitalistic structure, while poverty can't be defeated until that structure is replaced by some form of socialism.
Ayres steers between these positions and comes down solidly behind the bank. He suggests changes, but he sees it as fundamentally a ''reformist'' institution that has succeeded.
This book is not for the casual reader. It is by no means entertaining. It has been produced with something near the rigor of an article for a scholarly journal; the general reader may sometimes find it irritatingly obtuse or discursive, though occasional quotations from the author's hundreds of interviews with bank employees pep it up. It is painstakingly researched and thorough, and will be appreciated by the serious student, whether in or out of academia.