purred by memories of Sept. 11, more than a dozen states are beginning to acquire potassium iodide pills to protect people living or working near nuclear plants from potential radiation exposure should a terrorist attack or accident occur. Both those who are apprehensive about a terror attack and those who think, as we do, that the likelihood of a successful attack is small should welcome any effort to stockpile potassium iodide as a sensible precaution. The pills carry little risk except to those with iodine sensitivities, thyroid problems or certain rare conditions. They provide substantial protection against thyroid cancer if taken just before or within a few hours after exposure to radiation.

The pills will not prevent harm from all the radioactive constituents of any plume that might emerge from a stricken plant. They protect only against the uptake of radioactive iodine by the thyroid. But that is no trivial matter. Studies after the 1986 accident at the Chernobyl nuclear plant in Ukraine found that thyroid cancer, especially in young children, was overwhelmingly the worst consequence to public health. Children lucky enough to be given potassium iodide largely escaped harm.

The Nuclear Regulatory Commission has offered the pills free to any of the 34 states with people living within 10 miles of nuclear power plants. Thus far 13 have accepted, including New York, Connecticut and New Jersey. Westchester County began distributing pills to residents living within 10 miles of the Indian Point nuclear reactors last Saturday. The pills are also available over the counter at some drugstores, and on the Internet. Since prompt administration is critical, it makes sense to have supplies available at home, in schools and workplaces or at dispensing sites that can be reached quickly.

Health authorities stress that no one should start popping pills until officials evaluate a plume and issue instructions. Adults over 40 should take the pills only if the predicted exposure is high enough to destroy their thyroid, which may not happen.

Nuclear advocates fret that making the pills available will exaggerate public fears, while nuclear critics worry that the pills will breed complacency about nuclear risks. Federal and state officials stress that the pills are only a supplement to other measures to mitigate any danger, not a substitute for them. It remains vitally important to ensure the security of nuclear plants and to provide sound evacuation plans.