THE UNITED STATES persists in treating the

World Bank as though it were the competitor of the privately owned commercial banks. The Reagan administration seems to think of World Bank loans to the Third World as simple public subsidies --the international equivalent of welfare--while commercial bank loans represent the desirable discipline of private business. In fact, the genius of the World Bank has been its ability to collaborate with private lenders to supplement their resources, to enforce conditions on loans and to reduce the risks in international banking.

Political reality sharply limits the pressure that a commercial bank--particularly an American bank --can bring to bear on the government of a Third World country with a delinquent loan. It's very easy for governments to raise a cry of imperialism and dollar diplomacy. It's harder for them to bring that kind of accusation against a World Bank delegation that might be made up of, say, two Indian economists and an Argentinian engineer. No loan to the World Bank has ever been defaulted. When the World Bank participates in a development project, it provides a real measure of reassurance to the commercial banks that are also participating. If the United States were to diminish its support for the World Bank, it would not only reduce developing countries' access to concessional--that is, subsidized--credit. It would reduce their access to commercial credit as well.

When Secretary of State Alexander Haig was at the United Nations last week, he spoke as though all but the poorest countries could turn to greater reliance on commercial bank credit. But in most of the rich countries, financial authorities have begun to caution the commercial banks about the heavy debts of the developing countries. A few days ago Henry Wallich of the Federal Reserve Board pointedly and publicly suggested that it is now necessary to slow down the expansion of those debts. Many Third World countries managed to maintain rapid economic growth through the turbulent 1970s by increasingly heavy dependence on bank credit. That pattern won't survive far into the 1980s. What can the World Bank do to help?

One possibility might be the World Bank's much- debated energy affiliate, and the United States is simply and flatly wrong to try to kill it. The official American view assumes that it's a socialist scheme to displace private initiative. In reality, it's an attempt to get heavy private investment into parts of the world unaccustomed to it and utterly suspicious of it. Most Third World governments fear being cheated by the oil companies. Most oil companies fear nationalization in those countries if their exploration should be successful. By becoming the third partner at the table, the World Bank would offer reassurance to both government and company against exploitation by the other. It's a strategy to accelerate oil exploration in regions where there's very little of it--a point that does not yet appear to have percolated all the way through the administration here in Washington. The World Bank's meeting this week offers the Reagan administration a well-timed opportunity for closer acquaintance with an indispensable institution.