Regardless, he said, he considers the dangers of leaking chemical weapons in deep-water sites to be low.

He noted that the only Army chemical weapons dumpsite on nautical charts - the wreck of the S.S. William Ralston, scuttled 117 miles off San Francisco in the 1950s - hasn't been found to be leaking, though he said scientists have monitored it only "from a distance."

Not far from that wreck, scientists have determined that drums of radioactive waste dumped by industry in the 1950s have so corroded, they're now paper-thin - with holes in some of them, said Richard Charter, a California-based environmentalist with Environmental Defense.

He said he feared that recent congressional approval for offshore gas and oil exploration off the East and West coasts - permitted through this summer's lifting of a 22-year-old moratorium on the activity - could release the chemical agents from their containers.

"It certainly is within the realm of possibility," he said. "This is an invasive activity."

Seismic exploration is conducted by setting off huge airguns on the ocean surface and measuring the blasts when they bounce off the ocean floor. Such exploration and drilling operations have been conducted for decades in the Gulf of Mexico without releasing chemical warfare agents dumped by the Army in that body of water.

Overseas, scientists who monitor chemical weapons dumpsites off other countries have identified an unmistakable problem in the Skagerrak Strait, a narrow but deep body of water that separates Norway and Denmark.

In 2002, Norwegian scientists sent a remote-controlled vehicle to investigate four ships full of captured German chemical weapons. The U.S. and British militaries scuttled them after World War II in about 2,000 feet of water.

The Norwegians found that the sunken ships remained intact. Some of the shells had leaked. Others were slowly corroding. That reveals a problem that could last hundreds of years, the scientists concluded.

Soil sediment showed high levels of arsenic, a component of some of the chemical weapons. Arsenic is bioaccumulative. This means bottom-feeding shellfish are likely to be contaminated and pass arsenic up the food chain to accumulate in humans who eat them, the scientists learned.

Also worrisome: Nets from fishing trawlers were found tangled on some of the weapons-filled wrecks.

"It might be possible to get chemical ammunition in the nets, which could then be brought up to the surface and poison fishermen," the scientists wrote in a report on the expedition.

"It is also a possibility that fishing equipment could damage the wrecks and expose the chemical ammunition to the water, increasing the release of the agents to the environment."

The Army is obliged to at least assess the danger that the dumpsites pose today, said Lenny Siegel, director of the Center for Public Environmental Oversight who specializes in chemical weapons issues.

"If no one does a study looking for three-legged fish, how do they know it's not a problem?" he wondered.

"My guess is the risks are remote in most cases, but I think you have to at least evaluate the risk. They have to take continuing responsibility.

"They need to see if there is an impact on the food chain. If there is, you have to warn people. If so, they have to do something with them."