WASHINGTON — Since the 1980s, the Pentagon has relied increasingly on the super-hard, super-dense qualities of depleted-uranium metal, using it in tank shielding and armor-piercing munitions. And much of it is fouled with traces of plutonium and other dangerous radioisotopes.

The Army got word of the problem in August 1999, when the Department of Energy told commanders that the depleted-uranium armor in the latest Abrams tanks was made with recycled material contaminated during nuclear weapons production. The Army quietly studied 60 samples of the tainted metal before concluding early last year that "the presence of these trace radionuclides in armor is safe."

This year, amid charges that U.S. and NATO troops were sickened from exposure to depleted-uranium "tank-killer" munitions in the Persian Gulf War and the Balkans, the Pentagon revealed publicly that the bullets were made from contaminated metal. Although federal studies suggest that workers who made the recycled uranium metal may face heath risks, military officials insist that the contamination posed no threats in the finished military products.

Even so, at least two branches of the service have abandoned use of the controversial munitions.

The Pentagon's troubles with the contamination have intensified a heated global debate on the use of munitions and military hardware made with depleted uranium, so-called because much of the uranium's natural radioactivity was sapped when it was fed into nuclear reactors to make weapons fuel.

Studies to date support the contention that the levels of contaminants in depleted-uranium metal are tiny and account for little, if any, increase in the already low risks normally associated with the material. Depleted uranium produces a roughly 1% increase in the "background" radiation people normally absorb from sunlight and other natural sources.

But many veterans, environmentalists and public health officials are unconvinced. Their skepticism is heightened by the Pentagon's failure to announce the contamination of munitions and tank armor for more than a year after it learned of the problem. Some experts recommend more study of the mix of radioactive substances.

"You need to check to see if there's a cocktail that includes some of these more radioactive (contaminants)," says Malcolm Grimston, a senior fellow specializing in chemical and nuclear studies at the Royal Institute of International Affairs in London. "You need to redo the calculations."

Munitions appear to be the most widely used military product containing depleted uranium. U.S. forces fired more than 300 tons during the Gulf War. Iraq claims the spent rounds littering its land caused broad environmental damage and increased cancer rates. The same armor-piercing munitions were used extensively by U.S. and NATO warplanes during the 1999 bombing of Kosovo. That prompted ongoing risk studies by NATO and the World Health Organization.

The stakes are high, given depleted uranium's wide military use. A draft document prepared by the Energy Department in 1999 and obtained by USA TODAY shows that the fouled material was shipped to at least 50 U.S. military installations, foreign and domestic, for various uses, ranging from the tank armor and munitions to counterweights in military planes and ships.

Pentagon officials say substantial precautions are taken in using depleted uranium, but there have been problems. In 1999, for example, a maintenance bay at Robins Air Force Base in Georgia was contaminated with mildly radioactive dust after a technician used a hammer to break counterweights made of depleted uranium off a C-141 cargo plane. Urine and blood tests were done on the technician and other workers, but no harm was reported.

Amid all the controversy, the Navy and Marines have decided to abandon use of the depleted-uranium munitions. Both have switched to tungsten, a non-radioactive, high-density metal.

"We're not considering depleted uranium anymore because of the environmental problems associated with it, be them real or perceived," says Col. Clayton Nans, head of the Marines' Advanced Amphibious Assault Vehicle program and former chief of the service's firepower division. "We don't want to be in a position of having someone say, 'You can't bring your armor piercing rounds on the battlefield.' "