FOR more than 20 years superpower arms control efforts have focused on finished nuclear weapons. But the arms race might be limited by another approach: turning off the spigot of nuclear materials from which these weapons are made. This is an old idea that's been getting a new look in Washington in recent months. The aged US nuclear materials infrastructure has been shut down for safety reasons for more than a year, and some experts argue that the pause might as well be made permanent.
Advocates of this approach are focusing on several materials for possible control:
Plutonium and enriched uranium. These radioactive metallic elements are the heart of nuclear explosions. Since World War II the United States has produced some 100 metric tons of plutonium, but the last plutonium-producing reactor at Savannah River in South Carolina is now inactive.
An ``International Plutonium Control Act'' is now under consideration in Congress. Pushed in the Senate by Edward Kennedy (D) of Massachusetts and in the House by Foreign Affairs Committee chairman Dante Fascell (D) of Florida, the bill would cut off funds for new plutonium or enriched uranium production - if the Soviets agree to do likewise.
In April Soviet leader Mikhail Gorbachev announced he was shutting two Soviet plutonium plants. At the time Bush administration officials pointed out that 12 others remain in operation.
Tritium. This radioactive isotope of hydrogen is used in warheads to enhance blast power. It's perishable - decaying at the rate of about 5.5 percent a year. Thus existing warheads must be periodically recharged with the material.
The Bush administration wants to build two new tritium production reactors. But at a recent congressional hearing Carson Mark, former theoretical-physics division leader at the Los Alamos National Laboratory, urged that legislators not fund the reactors, as ``there is not an imminent tritium crisis.''
According to Dr. Mark, tritium removed from warheads being retired could largely supply US needs for several years - especially if a new arms pact limits the number of strategic nuclear warheads.
Controlling nuclear materials would not eliminate nuclear weapons. Plutonium essentially never decays, and thus could be reformed into new warheads. Weapons can be designed to work without tritium. But nuclear-materials control could ``put a rough cap on how many warheads you can build,'' says David Albright, a senior scientist at the Federation of American Scientists. It could make verification of deep cuts in nuclear weapons easier.
Administration officials say nuclear-materials control is irrelevant and diverts attention from the central issue of negotiating limits on the weapons themselves.
They worry that Congress will cut funds for what they say is the badly needed renovation of the US nuclear-materials infrastructure. ``We need two new reactors on line. There is no room for error,'' Robert Barker, assistant defense secretary for atomic energy, told Congress.