Mechanical bugs are plaguing a trial run of the Army's controversial chemical weapons incinerator, a prototype for a similar facility the Army plans to build at the Tooele Army Depot.

It's been a rough first few months for the Johnston Atoll Chemical Agent Disposal System, the first of nine incinerators planned to rid the United States of its aging chemical weapons. However, officials expect to finish destroying deadly stockpiles on site and en route from Germany on schedule.The high-tech weapons incinerator, criticized by Pacific island leaders and environmental groups, has operated just 22 percent of the time since testing began in June, officials said here Tuesday.

The $240 million facility was built to destroy 300,000 aging chemical weapons moved here from Okinawa in 1971 and 100,000 rounds being shipped from Germany - 6.6 percent of the U.S. stockpile - at this flat, windswept island 800 miles southwest of Honolulu.

The Environmental Protection Agency will decide whether to allow the Army to destroy more weapons after the test period is completed late next year. The operation is expected to wind up by 1995.

Charles Baronian, deputy program manager for JACADS, said officials had hoped to have the plant working 70 percent of the time during a 16-month testing period. Although the glitches won't doom the program, Baronian called them "very depressing for an engineer."

"It's not unusual for a brand new plant to have these kinds of problems," Baronian said. "However, we're seeing more of these types of problems than - frankly - we anticipated."

The main problem, Baronian said, is debris jamming a conveyor that carries parts of nerve gas rockets after incineration. Any breakdown in the system causes the entire facility to shut down, he said.

The mechanical glitches do not involve the release of nerve gas and do not endanger plant employees. Still, Baronian said plant managers would rather err on the side of caution and shut down for any problem, no matter how minor.

The Army will use what it learns from this plant at eight planned mainland incinerators which are to destroy all aging weapons by 1997, as required by Congress.

"I'm confident these lessons can be applied to those plants," said Brig. Gen. Walter L. Busbee, program manager for chemical demilitarization.

Along with Tooele, other plant sites are Umatilla, Ore.; Pueblo, Colo.; Newport, Ind.; Aberdeen, Md.; Anniston, Ala.; Lexington, Ky.; and Pine Bluff, Ark. The Army decided the safest plan was to build incinerators where the weapons are stored.