Army tests of M-55 rockets may add new insights in the debate over how - and how quickly - to dispose of the stockpile of aging chemical weapons.

Tooele Army Depot is home to 6,860 of the old rockets. Inspectors who make quarterly patrols through the storage igloos at TAD check the stockpile for rockets that are leaking deadly chemical agent. New "leakers" are discovered at the rate of six each quarter, on average.Whether leaking rockets could spontaneously explode has been an item of active debate by both the Army and military watchdog groups.

Bob Lockwood, military adviser to Sen. Orrin Hatch, R-Utah, said Thursday the Army conducted tests in New Jersey using simulated chemical agents and plans to conduct further tests in Maryland beginning in January using live chemical agent.

Tests using simulants showed no adverse reaction when the simulated agent came in contact with rocket propellant. In the next tests, "They will take live agent and combine it with propellant in a field test to see what the outcome is. They're predicting no explosion," Lockwood said.

The Army has used the rockets' potential instability as a tool to promote incineration. And a controversial $400 million incineration plant is nearing completion at TAD's south area.

An active group of opponents to incineration have said safety and environmental concerns outweigh problems the leakers may cause. They claimed a tactical victory in August when the Army conceded the rockets are more stable than it had previously thought.

The General Accounting Office, on the other hand, has a theory that agent mixed with propellant could lead to an explosion, Lockwood said. "Their theory needs to be validated or invalidated. That's why the Army is doing the study."

Leakers fall in one of two categories: those whose lethal payload escapes from the rocket and those where agent deteriorates a thin, aluminum membrane inside the rocket and allows the agent to come in contact with the rocket propellant. The latter type is the subject of the GAO's concern.

TAD spokesman Jeff Lindblad has said the M-55 leakers are among those in the stockpile that contain GB agent. M-55 rockets containing an agent called VX do not leak.

GB is highly volatile and evaporates quickly, especially at higher temperatures. VX, on the other hand, is described as having the consistency of motor oil.

"The testing is expected to take six to nine months," said Cathy Stalcup, spokeswoman for the Army Chemical Demilitarization and Remediation Activity. "Edge- wood Research, Development and Engineering Center will begin testing with live agent and propellant in January" under laboratory control.

"We have to plan for the worst case in this thing," Lockwood said. "If they find there is a potential for explosion, they'll have to set aside the chemical weapons (incineration) timetable and move immediately to the destruction of every M-55 rocket."

TAD stores 43 percent of the nation's chemical weapons stockpile and supposedly has almost 73 percent of all of the Army's leaking chemical arms. Other chemical weapons stored at TAD include weteye bombs, MC1 bombs, M23DX land mines and 105 mm, 155 mm and eight-inch artillery shells. The depot also has chemical agent stored in bulk containers.