RICHMOND - Officials at Blue Grass Army Depot and in surrounding counties staged an enormous drill yesterday to find out: If the unthinkable occurred, would they be ready?

To get the answer, they pretended that a disaster had indeed occurred. It involved an explosion, inside a storage building at the depot, that sent a plume of nerve gas drifting west toward Richmond.

Those who safeguard the chemical weapons stored at the depot say such an explosion is unlikely to actually occur. But the exercise staged yesterday, which involved more than 150 officials and untold numbers of area volunteers, left nothing to chance.

Officials gathered at Madison County's emergency operations center to answer phones, convey disaster information, and even type up fake press releases for people pretending to be reporters.

At the Richmond fire station on North Keeneland Drive, 19 students from Model Laboratory High School took decontamination showers in their bathing suits after their school bus was "exposed" to the chemical in Berea.

Their symptoms were runny noses, headaches and dizziness, said Celeste Roberts, a senior.

"I think it's really good for the community to be practicing and we're glad to do it," she said.

At Kirksville Elementary School, officials evaluated evacuation procedures. Workers at Berea Hospital duct-taped themselves into safety suits to prepare to decontaminate fake patients.

Nine counties participated, along with the state, the Federal Emergency Management Agen-cy, the Army and others. The exercises occur annually, but yesterday's was the largest and most elaborate yet.

"This is one of the things we don't stint on when it comes to money," said Richard Sloan, public-affairs officer for Blue Grass Chemical Activity, the agency responsible for safely storing the 523 tons of chemical weapons at the depot.

Officials will work through the weekend to evaluate the success of the test.

Connie Lawson, serving her first year as mayor of Richmond, seemed awestruck by the planning that went into the event and by the test itself.

"It was remarkable," she said afterward. "I feel much better prepared."