The World Bank "cannot do everything in the development field," and must not be regarded as "the Robin Hood of the international financial set," bank president A.W. Clausen said last night in a speech in Tokyo.

Clausen said that in the decade of the 1980s, the bank must be a "hard-headed, unsentimental institution that takes a very pragmatic and non-political view of what it is trying to do."

At the same time, he acknowledged that the bank's prudence and conservative nature would have to be balanced "by creativity and inventiveness as well" to meet the challenges of the next few years.

The basic objective is to assist countries receiving bank aid to accelerate economic growth and enhance the economic opportunities of their populations, he told the Yomiuri International Economic Society. A text of the speech was released here.

Clausen added that the bank can pursue its mandate successfully "only if it retains the support of the governments and private markets of capital-exporting countries."

The World Bank and other multilateral development banks are under pressure from the Reagan administration to trim sails, and to emphasize joint operations with the private sector where they can. A Treasury report detailing a new U.S. policy along these lines is due next month.

Clausen appeared to be walking a tightrope between non-well-publicized U.S. demands for an austere management and the pressures from the bank's poor-nation constituency for increasing help.

The main theme of his Tokyo speech was that rich and poor nations have indulged in an oversimplification that pits the interest of a so-called North against that of the South.

Clausen said that this bipolar concept of the international economy ignores the fact that "we are living in a multipolar would." He identified eight different poles, or centers, of economic activity, each with different problems, but each interacting with all the others.

In this complicated environment, the simple division of the world into rich and poor -- North and South -- no longer is helpful, Clausen said.

For example, one of the eight clusters he cited -- the 20 or so newly industrializing nations including Korea, Brazil, Mexico, and Malaysia -- once might have been considered part of the South. But these countries "on the move" are accounting for a greater share of industrial output, he said.

Counting Japan -- the model for some of the advancing nations -- this newly industrailzed group may account for more than one-fourth of would production by 1990, three times their percentage in 1960, he said. Meanwhile, the older industrial group in Europe and North America, which has more than two-thirds of would output in 1960, will drop to less than a 50 percent share by 1990.

Meanwhile, the bank announced that its director of policy planning, Mahbub ul Haq, 47, is returning to Pakistan as minister of planning and head of the Pakistan Planning Commission. Haq has been on the bank staff for the past 12 years.