It was about as bad a nightmare as Metro could have dreamed up for itself: 10 dead, 190 injured when a Virginia-bound subway train derails and catches fire 60 feet beneath the Potomac River.

It all happened last night -- in make-believe -- as Metro, the D.C. and Arlington fire departments and 10 area hospitals ran a simulated "worst-case" exercise to gauge how well they would be able to handle a real-life catastrophe of that magnitude.

D.C. fire officials labeled the operation a success and called their firefighters' performance "marvelous," as 200 "passengers" aboard the train were rescued unharmed. But Metro officials, who have been especially sensitive about safety issues since three persons were killed in a subway crash here Jan. 13, were less laudatory.

While agreeing that the exercise went smoothly in general, Metrorail chief Joe Sheard suggested, however, that D.C. firefighters could have moved faster.

"We will have to work to improve our response time," said Sheard, who was in the "accident train." He said he counted 32 minutes between the sounding of the first alarm and the arrival of the first firefighters. "I'm a little concerned about that," Sheard said.

But D.C. Fire Chief T.R. Coleman said his men were ordered to take their time and check out procedures carefully. In the event of a real emergency, he said, "we tend to move a little faster."

About 1,000 persons, including hundreds of observers and passenger volunteers, took part in the enactment, Metro's largest ever of a rail disaster.

The drill began with the crowded "accident train" leaving Foggy Bottom station at about 8 p.m. Aboard, playing the parts of passengers, were 200 Metro employes and 200 medical students from George Washington University, many of them wearing torn clothes and daubed with simulated blood.

Also aboard the train were Metro General Manager Richard Page and scores of observers from other transit systems and health service agencies.

The drill was about an hour late starting, due in part to a disruption of Metrorail's regular scheduled Sunday service earlier in the day caused by a smoke detector alarm activating near the Court House station.

Under the catastrophe scenario, the train derailed at high speed near a pumping station that removes water and which has a small passageway linking the parallel inbound and outbound tunnels used by trains. In reality, the train was merely stopped in the tunnel and smoke was simulated with a fogging machine.

The "accident" alarm was sounded at 8:10 p.m. D.C. firefighters entered the subway at Foggy Bottom station at about 8:18 and at 8:30 rode a "rescue" train toward the accident site using the other track.

Disembarking in the tunnel, they approached the accident train through the passageway at the pumping station, put out the mock fire and began evacuating people assumed to be unhurt or those "injured" but able to walk.

Arlington County firefighters, meanwhile, rode another rescue train from Rosslyn and took aboard passengers simulating serious injuries. D.C. firefighters also made a second trip back to the accident site to remove "seriously injured" passengers to Foggy Bottom before the drill concluded.

On the station platform, the victims, many of them with startlingly grisly "injuries," were laid out on bright orange stretchers, given emergency treatment, then taken to area hospitals. There the drill continued, with the injured being "admitted" or "treated and discharged."

Metro officials said last night's drill was Metro's 18th accident simulation. Metro has been trying to upgrade safety and rescue procedures since a crowded rush-hour train derailed last Jan. 13, killing three passengers.

Metro investigators laid primary blame for that crash on employes who were operating and overseeing the train but acknowledged that training and some emergency procedures were deficient.

Page said last night that the drill gave authorities an oppurtunity to test new communications equipment, a new-style evacuation ladder to replace ones that proved deficient during the Jan. 13 accident, and a new cart on which rescue equipment could be rolled into a tunnel.

Meanwhile, a special Metro board committee is reevaluating Metro's longtime policy of placing no instructions in cars to enable riders to let themselves out in an emergency.

Metro's position has been that in the great majority of accidents, it would be safer for passengers to wait for rescue workers than to leave the train themselves and risk the third rail's 750 volts or being hit by another train.