A confidential document prepared by the World Bank has concluded that predictions of global warming are too uncertain to justify limiting loans for development in Third World countries on environmental grounds alone.

The internal memorandum, which is expected to be the basis of a policy statement to be announced by bank President Barber Conable Sept. 11 in Tokyo, comes at a time when the Washington-based international development bank is under growing pressure to use its financial leverage to help direct economic development projects in ways that do not harm the environment. The World Bank is a major source of loans to less-developed countries.

Under Internal Pressure

Meanwhile, many poorer nations are under internal pressure to raise the standard of living for their burgeoning populations and improve their economies. Many of these Third World countries argue that industrialized countries are primarily responsible for such environmental problems as the greenhouse effect and should bear the brunt of solving them.

But the confidential memorandum, which outlines options for addressing the greenhouse effect issue, said the bank's Third World lending policies should aim for "immediate and obvious" economic benefits "without having to deal with the issues of uncertain global externalities." The paper, obtained by The Times, called scientific predictions of a global climate change "conjectural."

The document, which reportedly has been viewed favorably by senior bank officials, is expected to be incorporated into the bank's first comprehensive policy on the greenhouse effect, which is likely to be announced by Conable in a major environmental speech at an international conference on global environmental issues in Tokyo.

Seeking Billions of Dollars

The policy statement comes at a time when the bank is seeking billions of dollars in additional financial support from the United States and other industrialized countries to fund low-cost loans to developing countries. In 1987, when industrialized nations were last asked to contribute to the loan fund, $12.4 billion was pledged. The U.S. share was $2.8 billion.

The Bank is currently the largest single lender for Third World energy development, dispensing an average of $3.2 billion a year for the past five years.

The policy is likely to be welcomed by developing countries that do not want to sacrifice development necessary to meet the needs of their populations in order to stave off longer term global environmental problems.