THE ADMINISTRATION has adopted a new plan to make it easier for other countries to obtain plutonium through the reprocessing of U.S.- supplied nuclear reactor fuel. It is part of a policy to "re-establish a leadership role for the United States in international nuclear affairs." It is the policy that used to be called nuclear non-proliferation.

Under Presidents Ford and Carter, the American government attempted to discourage reprocessing of reactor fuels on grounds that reprocessing was not economically justified and that there is an immediate proliferation risk inherent in a technology that converts bulky, highly radioactive, hard-to- handle spent fuel into compact amounts of easy-to- handle, pure, weapons-usable plutonium. In support of this belief, the government indefinitely deferred its own reprocessing plans and further signaled its opposition by retaining, as a condition of sale of nuclear fuel, the right to decide whether that fuel could be reprocessed and the plutonium returned to its owner.

Countries that wished to reprocess U.S.-supplied fuel had to apply for case-by-case approval. If the reprocessing were to be done outside their own borders, they had to apply again for permission for the plutonium to be returned. The procedure was intensely irritating to other countries, not least because, after long delays, permission eventually was always granted.

Nevertheless, it was a good policy. It forced nations with young nuclear programs to look twice and three times at the accepted wisdom that reprocessing was the only way--or even a good way--to dispose of spent fuel. And it led nuclear suppliers to change their policies of exporting reprocessing plants and similar technologies with a very high proliferation risk to non-nuclear weapons states. Sales of reprocessing plants by France and Germany to Pakistan and Brazil, respectively, were canceled, and no similar sales have been made since.

Finally, and most relevant to the actions of the current administration, which has re-embraced reprocessing for the United States, the requirement for case-by-case approval gave this country continuing leverage over the nuclear behavior of those to whom it sold nuclear fuel. That leverage was exercised, to cite one instance, to induce Switzerland to put a stop to certain dangerous exports being made to Pakistan by Swiss companies.

There are decided limits to this sort of leverage. It must be used with great discretion, and when it is used there is no denying that it exacts a political cost. But it is an effective deterrent and, yes, an exercise of power that on occasion can be made to large and good effect. With its new policy, the administration has unilaterally relinquished this tool, and gained nothing in return.