But the scientists said that perchlorate - which is also found in fireworks and road flares - is nowhere near as safe as the Pentagon and the defense and aerospace industries have been telling Americans for years.

The National Academy of Sciences was called in to referee the dispute over the safety of the chemical. On one side were the strict standards proposed by the Environmental Protection Agency and several states; on the other were the Defense Department, the Department of Energy, NASA and industry, which called for standards considerably more lenient. The academy settled on a middle range of what levels of contamination are acceptable, and that appears to be a big win for industry.

The White House was evaluating the report on Monday but had no initial problems with it. "The national academy is the gold standard of independent scientific review," White House science spokesman Bob Hopkins said. "We respect the findings of this report."

The academy's proposed safe level for perchlorate is high enough that the vast majority of the 250 areas with tainted water won't have to do anything. This would save the Pentagon and defense and aerospace industry billions of dollars in potential clean-up costs.

Perchlorate, a compound that keeps iodide from being absorbed by the body, has been found to damage fetuses and infants and could lessen brain development and lead to attention deficit disorder. The Food and Drug Administration has found it in grocery stores' milk, according to a study last year.

R. Thomas Zoeller, a key scientist who advised the EPA, and an environmental group said the academy's study set the level too high to protect public health. And the environmental group, Natural Resources Defense Council, charged the Pentagon and White House tried to influence the academy study to keep the cost of clean-ups to a minimum - a complaint the White House and the academy denied.

The proposed safe dose level proposed by the academy "lets industry off the hook for clean-up and a lot of liability," said Jennifer Sass, senior scientist for the council.

The head of the defense industry's perchlorate study group didn't return several calls for comment. Rick Pleus, a scientist funded by the industry group, said he was assessing the report but was pleased by an early reading of the findings.

The academy said the safe dose level for perchlorate is about 20 times higher than the EPA proposed in a 2002 rule. Still, that level is up to 14 times lower than defense industry-sponsored studies say is safe.

The academy's level "should protect the health of even the most sensitive population," said Dr. Richard Johnston Jr., chairman of the panel and a pediatrics professor at the University of Colorado School of Medicine.

In 2002, the EPA proposed a safe drinking water standard of no more than 1 part of perchlorate per 1 billion parts of drinking water. The academy's recommendation would translate to about 20 parts per billion. The defense industry has argued for a level of 200 to 350 parts per billion.

California, which has a pervasive perchlorate pollution problem, has set a drinking-water standard of 6 parts per billion, but it's considering increasing that to one nearer to academy levels. Massachusetts, Maryland and New Mexico have proposed levels of 1 part per billion levels. New York permits a range of 5 to 18 parts per billion. Nevada has the highest state level, with 18.

The median level of perchlorate pollution in the United States is 6.4 parts per billion, with Jacksonville, Fla., reaching 200 parts per billion, according to the academy study.

According to Johnston, it isn't possible to measure perchlorate contamination at less than 4 parts per billion. And 96 percent of America's water systems have levels below that.

Before the national academy released its report Monday, the Natural Resources Defense Council accused the Pentagon and White House of trying to lobby the academy and change its study. The council relied on more than 30 boxes of documents it received through the Freedom of Information Act, but much of the documents were redacted, so the group based most of its charges on e-mail subject lines between Bush administration officials.

Council attorney Erik Olson called it "a full-scale assault by the Pentagon and its contractors."

"There's absolutely no basis for those claims," White House science spokesman Hopkins said. "This is an attempt to distort the science by attacking the process."

On the Web:

For more information, check out the following Web sites:

The National Academy of Sciences report:

http://www.nap.edu/catalog/11202.html

EPA's perchlorate Web site:

http://www.epa.gov/safewater/ccl/perchlorate/perchlorate.html

The Natural Resources Defense Council on perchlorate:

http://www.nrdc.org/media/pressreleases/050110.asp

An EPA Power Point presentation that includes a map of perchlorate problem areas can be found at:

http://www.epa.gov/tio/tsp/download/2004_fall_meeting....