Production of nuclear weapons in the entire U.S. 16-plant complex in 12 states has come to a halt. This is not the result of any treaty with the Soviet Union, but because of aging plants and safety concerns due to a four-decade buildup of radioactive contamination.

Four plants in Colorado, South Carolina, Washington, and Ohio are closed because of safety problems. These key closures have brought the rest of the production system to a standstill.The shutdowns have not endangered U.S. security. With nuclear warheads numbered in the thousands, there are enough such devices - more than enough - for now. But what about the future?

The massive modernization and cleanup of this problem will be expensive. The Department of Energy estimates it will cost $150 billion over the next 30 years.

Yet before the nation is committed to spending that staggering sum, this is a good time to review the future of the nuclear weapons program, what kind of facilities are needed, whether it is worth cleaning up some of them, what environmental rules should be applied to such plants, and what to do with radioactive waste.

The DOE is making a start on this project. Its "2010 Report" outlining a long-term plan for modernizing aging plants, is due to be submitted to Congress Dec. 14. By Dec. 31, the DOE should release another report listing the extent of contamination at its nuclear plants and setting priorities for cleaning up the most dangerous ones.

It may not be feasible to clean up the worst plants. Experts say the Rocky Flats plant near Denver, which makes plutonium triggers for warheads, is so contaminated that it may have to be abandoned, a permanent monument to radioactive danger, with barbed wire fences and guards.

Other questions that still must be resolved are environmental rules for nuclear weapon plants. So far, the DOE has successfully fought to keep the plants from being covered by general environmental law. Perhaps it's time to change that view. If new plants are going to be built, they are going to have to be kept cleaner.

What to do with radioactive waste has still not been fully resolved. Opening of a pilot project in New Mexico to store nuclear weapons waste has been delayed because of concerns over design and safety, plus the need for DOE to have total ownership of thousands of acres surrounding the facility.

For more than 40 years, the U.S. has lived in the nuclear era. It's past time to take a clearer look at where the nation is going in this regard, what is needed to keep building nuclear weapons, whether the nation is prepared to pay the cost, how much radioactive waste will be created, and where it will be stored.

These issues are not simply environmentalists versus weapons makers. It's not just "no more bombs" versus national security. It's more complex than that. There are trade-offs that must be made.

The problems require thoughtful study and some long-range perspective on nuclear policy - what the nation needs and how to get there at the least cost and with the least amount of risk.