For weeks, high-level discussions between federal and state environmental officials and the Defense Department have produced no solutions about how to treat a Harford County town's contaminated drinking water.

Military training exercises at Aberdeen Proving Ground, a key center for Army testing and research, have left most of the city of Aberdeen's wells tainted by perchlorate. The chemical, which is used as a propellant, impairs thyroid function and is suspected of contributing to developmental problems in fetuses, infants and young children.

As it negotiates cleanup of Aberdeen's wells, Maryland is being drawn into a national dispute over perchlorate, a saltlike compound detected in ground water in 21 other states from Massachusetts to California.

The major question facing states is this: How much perchlorate can people safely ingest? The Environmental Protection Agency, the Maryland Department of the Environment and the Defense Department have not reached a consensus on the standard to be allowed.

So, states are setting their own advisory levels - with Maryland and Massachusetts having the nation's lowest. The standard is critical in Aberdeen and across the nation, because the lower the level allowed, the higher the cleanup cost. It could push Defense Department spending into the billions of dollars instead of millions.

But without an EPA-determined national limit for perchlorate in drinking water, the military's response has been blunt: No standard, no cleanup.

"The battle line is really being drawn between EPA and DoD," said California lawyer Barry Groveman.

In Aberdeen, a community group that monitors cleanup at APG has written Maryland senators, Gov.-elect Robert L. Ehrlich Jr. and EPA Administrator Christine Todd Whitman, decrying the drawn-out discussions between state and federal officials as "sending the wrong message to the DoD."

The Defense Department argues that the message on perchlorate is simple: Research has not clearly defined a public health hazard.

"I don't think anyone is satisfied with the level of scientific information on perchlorate," said John Paul Woodley Jr., assistant deputy undersecretary of defense for environmental matters.

He was surprised when asked how the military would respond to a cleanup order in Maryland of 1 part per billion, the state's current advisory level.

"I would not expect them to propose anything along those lines," he said. "I would expect us to continue ... discussions about what action, if any, is appropriate under these circumstances."

Protecting citizens

But Robert S. Summers, director of MDE's Water Management Administration, said last week that EPA research led his agency to issue the 1 part per billion advisory level for perchlorate in August, and that there were no plans to revise it.

"Based on EPA work, we think the science is there to say 1 [part per billion] is a safe level," he said.

"We're trying to protect our citizens," Summers said. "We want the Army to clean up the contamination. We don't want these levels to get any worse."

Contamination in Aberdeen's well field ranges from 5 parts to 14 parts per billion.

Asked if the Defense Department would sue the state or appeal a cleanup decision, Woodley said: "I would not speculate on that."

Summers said he hopes it won't come to that.

"We're working with the Environmental Protection Agency and APG to try to come to a resolution," he said. "We haven't achieved that to this point."

EPA appears to be years away from issuing a standard - known as a maximum contaminant level, or MCL - for perchlorate. MCLs are used to define cleanup standards. Right now, the chemical is wending its way through EPA reviews.

But there is wide-ranging disagreement over any figures, which are measured in parts per billion - a hard-to-imagine number for the average person.

One part per billion is equivalent to about one drop of water in an Olympic-size swimming pool, said Will Humble, chief of the environmental health office in the Arizona Department of Health Services.

"It sounds so infinitesimal, but it can be so important," he said. "Every compound has its own toxicity."

An Air Force toxicologist meeting with water utility officials last month in Ontario, Calif., posited 70 parts per billion of perchlorate in drinking water as an acceptable limit; California officials, on the other hand, are considering a limit of 4 parts per billion. Several states, including Arizona, have advisory limits as high as 14 parts per billion.

If Maryland orders a cleanup to 1 part per billion, communities in other states could demand the same treatment level, said Kevin Mayer, a scientist in EPA's Pacific Southwest office.

At any site, the amount of water requiring treatment increases significantly as the maximum contaminant level decreases, Woodley said.

"The lower it gets, exponentially, the costs will increase," he said.

So will the number of sites requiring treatment.

Perchlorate has been used for decades as an oxidizer in jet and rocket fuels. The chemical is also used in the nuclear and space industries, and in fireworks. Only eight states have no known manufacturers or users.

While the Defense Department is not the sole consumer of perchlorate, the explosive salt is widely used by the military to jump-start smoke grenades, jet fuel and other incendiary devices.

In Massachusetts, the military is committed to a $300 million cleanup around Cape Cod's Massachusetts Military Reservation that includes perchlorate remediation, said Joel Feigenbaum, a community college mathematics professor and activist. Perchlorate levels as high as 300 parts per billion have been found in the area's ground water, he said.

In San Bernardino County, east of Los Angeles, one water district has found 820 parts per billion of perchlorate in its wells. The Department of Defense, private industries, a fireworks plant and a landfill have operated in the area.

Perchlorate has been found in 59 municipal water supplies in California, from Sacramento to Southern California, said the EPA's Mayer. He said the contaminant has also been found in Nevada's Lake Mead and the Colorado River, which irrigates more than 90 percent of the nation's winter vegetable crops and supplies water to as many as 20 million residents in Arizona, Nevada and California.

"Statewide, perchlorate's becoming a very serious problem," said Barry Groveman, a Los Angeles lawyer who heads the Perchlorate Task Force, a group formed several months ago that includes water companies, city governments, lawyers and other agencies.

Much more to learn

Much remains to be learned about perchlorate's effect on the human body, and those most vulnerable - fetuses, infants and small children - cannot be safely tested. Impaired thyroid function can cause retardation, hyperactivity and other developmental problems. Regulators and toxicologists say that until more is known, the perchlorate limit should be conservative.

Adding to the dispute is the fact that the studies that discount risks of perchlorate have been funded by the Defense Department, perchorate producers or the Perchlorate Study Group, which is constituted primarily of defense contractors. An Arizona health department study completed in 2000, however, suggested adverse health effects in newborns whose mothers were exposed to perchlorate in drinking water.

"It's a smoking gun; it's a real problem for the military," said Lenny Siegel, director of the Center for Public Environmental Oversight, based in California.

"The fear for the Army is that once they start looking for [perchlorate], they'll find more of it."

Groveman, the Los Angeles lawyer, said a class action lawsuit similar to the one filed by states against tobacco companies could be a way to force the military to act.

He said Defense Department efforts to fight cleanup and dispute safe perchlorate levels are unacceptable.

But Woodley said the military is acting appropriately under the circumstances.

"Apply common sense, don't panic and do the best you can," he said. "That's the policy that we're trying to apply here."