In a report expected to influence a final EPA regulation on the chemical, the National Academy of Sciences supported a level of contamination closer to that favored by the Pentagon, and not the more stringent rules sought by environmentalists and some Democrats.

The study comes after years of disagreement over how dangerous it is for people to consume water tainted with perchlorate, a pervasive leftover of Cold War defense manufacturing that has been found in drinking water in 35 states.

The EPA currently has no final pollution standard for perchlorate in drinking water. The chemical can inhibit thyroid function and is considered particularly dangerous to children.

The NAS panel recommended allowing a level roughly equal to 20 parts per billion in drinking water. Two years ago, EPA issued a preliminary recommendation of 1 part per billion. Parts per billion is a common water quality measurement.

Perchlorate is the explosive component of rocket fuel. It is used to manufacture fireworks, gunpowder and highway flares. It is also used in tanning and leather finishing, rubber, paint and enamel production.

The Environmental Working Group, a research group with offices in California and Washington, D.C., reports that perchlorate contaminates drinking water supplies, groundwater or soil in hundreds of locations in at least 43 states.

The America Pacific Corp., a Las Vegas-based company that owns Western Electrochemical Co. in Cedar City, is the only remaining manufacturer of ammonium perchlorate in the nation.

Since 1997, the state Department of Environmental Quality has identified three sites where perchlorate has contaminated groundwater in Utah: ATK Thiokol Propulsion's facilities in West Valley City and Promontory and Hill Air Force Base.

Last month, the federal Food and Drug Administration reported finding perchlorate in 217 of 232 samples of milk and lettuce in 15 states. The report was the first to document nationwide contamination of food.