Perhaps as many as one-third of those cancers could be avoided by reducing home radon concentrations below the "action level" recommended by the Environmental Protection Agency, a panel of the National Research Council concluded in a report issued yesterday. Approximately 6 percent of U.S. homes have radon levels above the EPA guideline.

Because it may account for about 12 percent of all lung-cancer deaths in the United States, "radon is an important public health risk and should be recognized as such," Samet said at a news briefing at the National Academy of Sciences here. The National Research Council is the principal working arm of the NAS.

The report stressed that about 90 percent of radon-related cancers occur in current or former smokers, and "most of the radon-related deaths among smokers would not have occurred if the victims had not smoked." Smokers are at greatest risk of lung cancer from radon exposure because the effects of the gas apparently reinforce those of tobacco smoke, producing a combined threat greater than cigarettes or radon alone.