In a statewide Y2K simulation exercise Thursday, emergency management staff in all three Southern Maryland counties made discoveries -- some major, some frivolous -- that could help the region deal with a variety of potential millennial glitches they may face as Maryland rings in the new year.

Calvert officials, for example, recognized after the simulation that they need a plan to provide backup heat at emergency shelters, should gas lines be cut off. They also realized they better keep handy the key to the soda machine so they'll be able to greet the new year with at least ginger ale, even without power.

For five hours Thursday, the Maryland Emergency Management Agency kept the state's 23 counties, plus Baltimore and Ocean City, busy with a series of possible Y2K scenarios, including a false fire alarm at the Calvert Cliffs Nuclear Power Plant and a downed plane in St. Mary's County.

The purpose of the exercise was to test the state's and local communities' ability to cope with unpredictable events that might unfold when the clock strikes midnight on Dec. 31. Because all computer chips may not have been updated, a few systems could misread the year 2000 as 1900 and malfunction or shut down.

At Calvert County's emergency operation center, a war room for natural disasters and nuclear emergencies, the exercise brought a mix of gravity and lightheartedness. Outside, it was a hot summer day, but inside, the simulation was set in the middle of the night in 15-degree weather.

At moments, the 30 or so people in the room -- representing police and fire, transportation, hospitals, utilities and other agencies -- were quiet and serious, eyes fixed on the charts and maps on the walls, ready to jump whenever one of the many red, black and beige telephones rang out. At other times, they cracked jokes about the scenarios, such as one in which a doctor and nurse were trapped in a stalled elevator.

But most of the time, they calmly discussed the proper response for each situation. And they handled all the imaginary crises with ease.

"We got very good remarks from the [state] evaluator," said Calvert Emergency Management Director Donald Hall. "He said it was the best he'd ever seen. Our staff is very . . . experienced, and we're very used to this kind of testing."

Emergency experts emphasized that the Y2K tests were designed to make communities think about dealing with worst-case scenarios. Experts are not necessarily expecting widespread jammed phone lines, broken traffic lights or power outages.

"We don't want the public to feel this is the way it's going to be," Hall said.

In fact, officials anticipate that the public itself may create the biggest problem of all. Inflated rumors could create panic and jam 911 lines, they suggest. Or simple curiosity might lead thousands of people to test the phone lines simultaneously, causing the system to crash.

In the Charles County simulation, county public information officer Nina Voehl found herself busy with "rumor control," setting up imaginary news conferences to correct a mistaken report that deadly gas had escaped from the Mattawoman Waste Water Plant.

While the Y2K glitches might never surface at all, county officials are sure they will have to handle one type of New Year's problem: revelers who become out-of-control, as some do every year.

"Its typical to get the yo-yo who's been partying too hard," Voehl said.

Officials in all three counties say they are deciding how much emergency personnel they will keep on staff over New Year's Eve.

They express confidence that their computers will be Y2K compliant and that they will have all the backup generators and communication lines necessary to keep emergency efforts running smoothly, no matter what happens.

"I really feel we're ready for it," said Paul Wible, director of emergency management for St. Mary's County.