The Army's prototype plant for destroying chemical weapons is 32 months behind schedule and will cost an additional $190 million or more, a congressional inquiry found.

Delays at the Johnston Island disposal facility in the Pacific Ocean also are holding up construction of three U.S. disposal sites that will rely on lessons learned from the prototype, the General Accounting Office said in a report released yesterday. The sites are at Anniston, Ala., Pine Bluff, Ark., and Umatilla, Ore.

The delays also will increase the cost of storing the nerve and mustard agents at the four locations by more than $33 million, the GAO said.

The report said Congress must blame itself for some of the delays and increased costs. The Army originally planned to destroy only one chemical munition, the M-55 rocket. However, Congress in 1985 ordered destruction of all the nation's chemical weapons, which forced a complete revision of the program.

Two years later, Congress required tests to demonstrate that the weapons and chemical agents could be destroyed while still meeting environmental requirements.

While full-scale operations at Johnston Island were originally scheduled for February 1989, the congressionally ordered expansion, the environmental testings and delays by a private contractor pushed the date back 32 months to late September 1991.

An Army spokesman said yesterday that the prototype plant began disposing of its first chemical weapons July 1.

Stocks on Johnston Island and chemical weapons removed from Europe should be destroyed by late 1994, he said. Chemical weapons stored at eight U.S. locations are scheduled to be destroyed by April 30, 1997.