Whenever plutonium is bought, sold and shipped from one country to another, that is grounds for concern. Switzerland had earlier sent some spent fuel from a nuclear reactor to France for reprocessing and now wishes to bring the separated plutonium back for use in its own nuclear program. Because the fuel originally came from the United States, the Swiss need American approval to move it. The important point here is not that the Swiss are proposing anything out of the ordinary, but precisely the opposite -- these shipments are becoming commonplace, and American approvals seem routine. They ought not be.

Plutonium is highly toxic, and, of course, nuclear weapons can be fabricated out of it. There's quite a lot of it around the world, most of it in the hands of the five countries that maintain nuclear armories. But their weapons are at least under military control. The movement of plutonium into the civilian economy as a fuel raises other kinds of anxiety. The more widely the stuff is dispersed among civilian power stations and laboratories, moving along the highways and rails, the greater become the chances of loss, theft, mishandling and misuse. In the absence of any compelling reason to expand the trade in plutonium, there's a pretty strong logic to keeping it out of circulation.

Switzerland has no nuclear weapons, nor any intention of developing them. Its interest in plutonium is solely in its potential for generating electricity. But it isn't really the power supply that's in question here. The early promise of the breeder reactor has faded, and it is only the breeder that requires plutonium fuel. Experience shows the breeder to be enormously costly and utterly uneconomical.

Why do governments spend large amounts of money to pursue research on the breeder, as Switzerland will do with this plutonium? Perhaps because it is a way of asserting a country's command of nuclear technology in general. Switzerland is a major producer of nuclear equipment and, unfortunately, it has not always been careful about its customers. Within the past decade the Swiss have sold equipment to Pakistan that may be useful to it in its attempts to build weapons.

A standard nuclear power reactor, using uranium as fuel, does not have large implications for the proliferation of nuclear weapons. The fuel won't make bombs. But when a reactor uses plutonium, the wall between nuclear power and nuclear weapons becomes frail and porous. That's why, in a world that has plenty of uranium, it is unwise for governments to mess around with plutonium fuels. It would be equally unwise of the United States to get into the habit of approving these international transfers of plutonium with nothing more than a nod and a shrug.