AS THE CASE for building the Clinch River breeder reactor grows steadily worse, the costs of building it go steadily higher. The appropriations bill containing Clinch River's money is about to come to the floor of the House of Representatives. That gives the House an opportunity to kill, at last, this wasteful and highly dangerous venture.

The debate is currently fixed on money, since the thing can best be reached through the fiscal legislation, and the costs are large. The Energy Department's current cost estimate is $3.6 billion, and the General Accounting Office's reviews suggest even higher figures. But there are further and larger questions here.

The breeder technology is risky, but its purpose is to extract perhaps 100 times as much electricity from the uranium as the present generation of light water reactors can. Are the risks worth it? This project first took shape in the late 1960s, when the government expected a huge expansion of nuclear power that would create a severe shortage of uranium. A decade ago, the GAO pointed out recently, the government expected 800 to 1,500 reactors in operation by the end of the century; its estimate currently is 145 to 185. Meanwhile, there have been huge discoveries of high-grade uranium ore around the world, and, far from facing a shortage, the American uranium industry is frantically urging Congress to pass legislation to protect it from imports.

There's a far better reason than money for killing the Clinch River reactor. Technology places a solid wall between the present power reactors, on one side, and the plutonium technologies, on the other. The present reactors run on a uranium fuel that cannot be made into bombs. Although its wastes contain plutonium, that plutonium can be extracted only by an extremely difficult and expensive process. But the breeder reactor requires plutonium as a fuel. Once recaptured to feed the breeder, it can easily be fabricated into weapons. The breeder demolishes that wall between nuclear power and nuclear weapons. The reprocessing plants that supply breeders have military implications, and the fuel has to be handled under military security -- not least to keep it out of the hands of terrorists.

If you support the principle of nuclear power as a clean and relatively safe way of generating electricity, you would do well to oppose admantly the construction of the Clinch River breeder reactor. Building this reactor would give substance to all of the most extreme fears about nuclear power and to the accusation that it inevitably puts the ready ingredients of weapons into everyday commerce. Plutonium would place on the nuclear industry and the utilities a burden that they cannot carry. Even if the reactor were less expensive and even if it promised cheaper power -- as it manifestly does not -- the breeder technology can bring only harm to the civilian economy.