BRUSSELS (Reuters) - Just when it thought it had the depleted uranium (DU) scare under control, NATO may face a fresh onslaught of concern as the United States belatedly confirms that some DU munitions contain minute traces of plutonium.

Uranium is one thing. Plutonium is quite another, especially if it arises from flaws at a problem-plagued U.S. nuclear plant.

Plutonium is a heavyweight in the lexicon of scare words -- according to media reports, a particle as small as a millionth of an ounce, if inhaled, can cause a fatal cancer.

German Defense Minister Rudolf Scharping last Wednesday took the highly unusual step of calling in the U.S. charge d'affaires in Berlin to seek more information -- after a German television network reported on the plutonium factor.

Washington can rightly claim that the plutonium issue was not a secret -- but its spokesmen have omitted to mention it.

U.S. experts brought in by NATO in the past 10 days to calm fears of a cancer risk from DU ammunition used in Kosovo, Bosnia and the Gulf stressed that DU is 40 percent less radioactive than the natural uranium people eat, drink and breathe.

What they did not say was that some DU comes from recycled nuclear fuel, not ore, and contains traces not only of highly radioactive uranium-236 but of plutonium as well.

A review of transcripts and audio files shows that U.S. Army medical experts flown from Washington failed to mention the word plutonium once. One, asked if DU might contain uranium-236, said: "I can't answer. I just don't know."

A NATO spokesman said pointedly that reporters were "getting exactly the same briefings as the NATO ambassadors just got."

Two days later, NATO had to issue a statement saying the presence in DU of U-236 and plutonium in minute quantities had "long been established" but was "irrelevant" as it did not increase the extremely limited DU risks openly acknowledged.

LINK TO TROUBLED NUCLEAR PLANT

The furor erupted over DU munitions in early January, but there has been no mention in NATO public records of serious safety failures at the Kentucky plant which made the material.

Last Thursday, as the Clinton administration bowed out, the outgoing Pentagon spokesman was asked about U-236 traces.

"As you know, we discovered some stray elements, transuranics they're called, in depleted uranium, the Department of Energy did, a year or so ago," Kenneth Bacon said.

"They consisted of plutonium, neptunium and americium. Now these are very, very small amounts and as soon as they were discovered as indicating possibly a flaw in production in the production process, the Nuclear Regulatory Commission suspended the operation at this plant, which is in Paducah, Kentucky."

Bacon said operations resumed after a 90-day examination.

"Now, the labs in Europe have found tiny elements of U-236, which is not normally in depleted uranium," he added. These were so small that United Nations scientists said they did not change the very low radiotoxicity of the depleted uranium...

"We're looking into how this could have happened."

NO DEFENSE AGAINST DOUBT

A World Health Organization team is going to Kosovo this week to take more samples in places where DU anti-tank rounds were fired by U.S. planes in the 1999 NATO campaign.

If plutonium shows up with any regularity, it may not matter that levels are too small to pose a serious health risk, as the United States and NATO insist: public doubt is likely to grow and opposition to the munitions will rise with it.

Even minute levels could fuel speculation that a "bad batch" of DU from Paducah contained more plutonium than expected, and may have been inhaled in dust kicked up later.

The Paducah plant, which has made nuclear weapons material for 50 years under government contractors, is being sued for $10 billion for concealing health risks from workers and locals.

A February 2000 U.S. Department of Energy report said the plant "operated in a climate of secrecy, with a strong sense of national need, and a lack of understanding of a number of environment, safety and health risks."

Workers had "become ill because of workplace exposures."

The Paducah plant was cited for scattering plutonium at 1,200 times the normal background level beyond its grounds and attempting to cover up this and other safety violations.

The U.S. Nuclear Regulatory Commission said 1,600 tonnes of nuclear weapons parts were littered around the grounds below ground and in ground-level storage areas.

STILL NO EVIDENCE OF SYNDROME

There is no proof of any mystery illness among NATO peacekeepers and no "Balkans syndrome" to be explained, the medical chiefs of NATO's 19 armies all agreed last week after a day of comparing records.

But the issue remains one of credibility as much as health. Finger-pointing could proliferate if governments faced renewed charges of not informing the public in good time of what some will suspect they knew all along.

The information is all available on the Internet from U.S. newspapers and groups using the U.S. Freedom of Information Act.

In a January 2000 letter to the activist Military Toxics Project, the U.S. Department of Energy said it believed minute quantities of plutonium might be contained in U.S. stocks of depleted uranium, but in amounts too low to pose risk.

It noted health and safety concerns at Paducah and said DU test rounds "almost certainly" contained recycled uranium but did not directly answer: did they contain plutonium?.

The Department's letter was recently passed on to NATO.

Neverthless, European governments appeared unprepared for media "revelations" about plutonium traces in DU rounds and at NATO there are differences about whether Scharping and others facing a media grilling should have known what to expect.

Defense Secretary William Cohen had said earlier this month that DU was no more dangerous than "leaded paint," and a U.S. Army briefer assured reporters it was safe enough to eat.

Now that the word plutonium has been mentioned, that may have been a public relations miscalculation.