THE D.C. Fire Department stepped up its attack on the safety of Metro subway cars yesterday when Deputy Chief T. R. Coleman told the National Transportation Safety Board that "there is an alarming potential for disaster in the Metro system."

Metro officials immediately disputed Coleman's statement and noted that the system has never had a fatal fire. "I would have to disagree with the chief on that one", said John J. Flynn, director of safety for Metro.

Coleman said in an interview that his primary concern is the polyvinylchloride plastic that is used for the interior walls of Metro's cars. pPVC, as the compound is usually known, is difficult to ignite but is highly toxic after it catches fire.

"We have had some problems with PVC," Coleman said. "We know it will kill you." Earlier, D.C. Fire Chief Norman Richardson, in a letter to the board, had expressed concern about flammable materials used in the subway. He cited the plastic walls and the ignitable neoprene used in the seat cushions of Metro cars. Richardson suggested that Metro have metal walls and metal seats to reduce fire danger.

Dramatic photographs of burned-out subways cars from San Francisco, Tronoto and Montreal were features of the board's two-day hearing on rail in transit fires, fire departments are concerned that some day a blaze will break out in a fully loaded car while it is trapped in a tunnel between stations.

Metro has had a number of undercar fires, none of which have penetrated the passenger area. Coleman said yesterday that one such fire had melted the first of several layers of flooring before it was extinguished.

In every case, Metro has been able to get the train to a station where passengers were quickly evacuated. Evacuation in a tunnel would be much more difficult and take more time.

Metro has on order 94 cars. They will have steel underflooring instead of aluminum, and steel is preferred by the D.C. Fire Department. But the interiors will be about the same as those on the present cars, Metro officials said yesterday.

Neoprene, not metal, is planned for the seats. Wool carpet will be used on the floors. According to the specifications, the walls will be of a substance that meets the fire standards established by the U.S. Department of Transportation. That could well be a polyvinylchloride compound, officials said.

Richard S. Page, Metro's general manager, said late yesterday that he has asked D.C. government representatives to set up a meeting between himself and Fire Chief Richardson to discuss the safety issues.

In a similar meeting last year between Page and then-Fire Chief Jefferson Lewis, Metro agreed to improvements in radio communications, tunnel markings, training programs and other items. "No questions were raised about the design or construction of the cars," Page said yesterday.

"I want to get back to cooperative relationships (with the area fire departments) and not criticize each other in hearings and newspapers," he said. d

Safely board chairman James B. King and member Patricia Goldman pressed officials from metro, Chicago and Atlanta yesterday on whether they shared their fire safety problems and learned from each other. Such sharing is informal at best, they learned. There is a lack of national fire standards for subway systems and no federal regulation, and King and the board are clearly questioning whether such regulation might be needed.

All the transit officials said that, in effect, guidelines would be all right, but they did not want to devote their safety staffs' time to filling our paperwork required by federal regulation.

Metro's Flynn said federal regulation could reduce safety because of the time it would take. The safety board's Goldman asked Metro officials to explain why they were making some of the safety improvements that they listed in their testimony.

Nicholas J. Roll, Metro's assistant general manager for transit services, said that some of the proposals had come as a result of a congressional hearing after a fire in Metro's Potomac River tunnel in April.

"I hope the [improvements] that come from congressional oversight won't degrade safety," Goldman said.