IN ITS MISDIRECTED enthusiasm for plutonium, the Reagan administration is doing more for the anti-nuclear movement than Ralph Nader, SANE and the Clamshell Alliance together. The fuel for a standard nuclear reactor can't explode. But the used fuel can be reprocessed--by a highly complex and expensive method of extraction -- into plutonium, out of which even an amateur chemist can build nuclear weapons. The Reagan administration is carrying on a fervent campaign to begin reprocessing.

The effect is, of course, to confirm everybody's worst fears about nuclear power, not to mention their worst fears about the Reagan administration. The Atomic Industrial Forum, the nuclear power trade organization, has been meeting here this week. The Department of Energy sent a representative to chide the businessmen bitterly for their failure to get behind the reprocessing technology and push.

He didn't get much of a response. The businessmen in the audience know perfectly well that the economic rationale for reprocessing has long since ceased to exist. The argument, a decade ago and more, held that reprocessing, though desperately dangerous, was essential to the national interest because the country's need for electricity was soaring and the supply of uranium would soon be exhausted. The solution, according to that view, was to reprocess the spent uranium fuel for the plutonium -- which could then be used to stretch the uranium fuel in power plants and eventually to fuel the breeder reactor. The prototype breeder was planned for Clinch River, Tennessee.

Since then, electricity requirements have dropped sharply. There have been gigantic discoveries of uranium, and the American uranium industry is now banging frantically on congressmen's doors for protection from imports. As for the Clinch River breeder, now severely obsolete, the only serious case for it is that it would generate construction jobs in a state represented in the Senate by the majority leader.

The right-wing fascination with plutonium is one of the true anomalies in current politics. Everything about the plutonium cycle violates conservative tenets. No part of the cycle can operate without gigantic subsidies. It would require stringent and highly detailed federal regulation, for the stuff is wildly toxic as well as explosive. It would impose an unprecedented centralization on the utility industry. The transport system would probably have to be federalized, since it would require security of a military character.

It's well understood that the Department of Energy has been in a state of intellectual receivership for the past two years. But isn't there anybody over there capable of pulling the switch to turn off a remarkably bad idea?