THE MOST important thing to be said about the Reagan administration's new nuclear energy policy is that, though its aim is to improve the climate for nuclear power, it could well make matters worse. By restarting the bitter debate over reprocessing and breeders at a time when the economics of both have never looked less promising, the new policy promises to divert Congress' and the industry's attention from nuclear power's pressing woes into another fruitless, prolonged stalemate.

The new policy reverses the Ford-Carter decision to postpone indefinitely commercial reprocessing-- the process by which used nuclear fuel rods are converted into plutonium and liquid waste. The policy adopted by the earlier presidents was made on two grounds: that reprocessing without breeders does not make economic sense and that the setting of an international example would slow the spread of weapons-related technologies and thereby enhance world security. The Reagan policy deals with the economic drawbacks of reprocessing by offering a limited subsidy in the shape of a purchase guarantee of whatever plutonium is produced. It deals with the second consideration not at all. Discussions in the course of preparing the new policy, says an administration spokesman, "did not go into the question of proliferation abroad."

The reprocessing decision creates a classic Catch- 22 for nuclear waste policy. Those in the administration concerned with cutting spending and opposed to government subsidies prevailed over those who wanted a much larger subsidy for reprocessing, especially the several hundred million dollars it would take to finish a reprocessing plant at Barnwell, S.C. No one seriously expects the government's purchase guarantee to be enough to entice private enterprise into this extremely risky and expensive business. But on the other hand, the Department of Energy succeeded in pushing its view that reprocessing is essential and that there should be no program for disposal of spent fuel rods--only of reprocessing wastes. But if there is no reprocessing and no spent fuel disposal, there will continue to be no nuclear waste program. Therefore, there will little hope of recapturing public and utility confidence in the future of nuclear power.

Mr. Reagan also decided to complete the Clinch River breeder reactor. Everything that can be said about Clinch River has been said many times in the course of the almost 10 years its fate has been fought over. It may be worth adding now only that, despite the president's decision, the reactor is unlikely ever to be built. The case for it is just too weak to justify the expenditure of the additional billion dollars that is needed. David Stockman, The Wall Street Journal and the American Enterprise Institute have all recognized that. Can Congress be far behind?

The best that can be said for the administration's new policy is that it demonstrates strong rhetorical support for nuclear power--nothing more, nothing less.