After the subway accident last Jan. 13 that killed three passengers, the idea of having emergency workers do disaster drills seems far more serious and urgent. So those who regularly ride Metro should welcome word that the D.C. Fire Department will conduct the largest test in history of the District's emergency response capability on Nov. 7.

Acting Fire Chief Theodore R. Coleman said the test will involve a simulated derailment of a train, resulting in 200 injuries, between the Foggy Bottom and Rosslyn stations, beneath the Potomac River. The test will be conducted an hour after regular Sunday train service shuts down at 6 p.m.

The exercise, conducted with Metro's cooperation, will require the proper removal and restoration of power in the third rail that powers Metro trains, along with proper use of ventilation, firefighting water standpipes, communications, control systems and a rescue train. The exercise also will test a plug-in telephone system recently installed in the under-the-Potomac tunnel.

Coleman said the D.C. and Arlington fire departments will spearhead the simulated rescue, aided by Alexandria and the Fairfax, Prince George's and Montgomery County departments.

Ten hospitals will participate. "Victims" will be provided by George Washington University. Walter Reed Army Medical Center personnel will help simulate injuries.

The Jan. 13 fatal accident, the first involving train passengers, occurred only minutes after the Air Florida crash near the 14th Street bridge that took 78 lives, overtaxing the city's available emergency capability.