Within 20 minutes after Air Florida Flight 90 crashed near the 14th Street Bridge Wednesday the 10-member "Go Team" of the National Transportation Safety Board's Aviation Division had set up a temporary command post in Hangar 6 at Washington National Airport and had dispatched investigators to the accident site.

About 10 minutes later the telephone rang on Harold Storey's desk at the agency's headquarters on Independence Avenue SW.

Storey, who oversees the NTSB's railroad investigation branch, was told that a Metro subway train had derailed near the Federal Triangle station. He went to the L'Enfant Plaza station and walked through the tunnel to the scene, where he started helping in the rescue. A few hours later a three-member NTSB team began investigating.

If it seemed as if the NTSB team members were taking the first major airline crash in 26 months and the first fatal Metro accident rather routinely, it was because tragedy is their business.

Major airplane and railroad accidents, large gas pipeline explosions and highway accidents that cause five or more deaths fall under the jurisdiction of the NTSB, one of the government's smallest agencies. It has about 325 employes and a budget of $17 million.

In 1980 the agency investigated 56 major accidents in this country and 27 abroad. Its 10 field offices conducted 1,539 investigations of more minor accidents.

The NTSB was created in 1966 as an autonomous agency within the Department of Transportation. But by 1974, safety board members were complaining about their agency's role. Being part of DOT, they said, made it difficult for them to criticize DOT policies. Congress agreed, and in 1975 the NTSB became an independent agency.

As part of its mission of investigating accidents to make transportation safer, the agency maintains two teams on call 24 hours a day, for ground and aviation accidents.

On Wednesday, Rudolf Kapustin's aviation team was on call. It was not the first time that Kapustin, a 20-year NTSB veteran, has been called to investigate a major air crash. He was the chief investigator in December, 1974, when Trans World Airlines Flight 514 crashed into a Virginia mountain, killing seven crew members and 85 passengers. That had been the last, major commercial airplane crash in the Washington area.

Kapustin's counterpart on the railroad team is John Rehor, another NTSB veteran who is a specialist, a spokesman said, in derailments and accidents involving hazardous wastes.

Each team also has one of the NTSB's five board members assigned to it. The board members, who are presidential appointees serving five-year terms, oversee the teams' operations.

Francis H. McAdams, a former Navy carrier pilot and aviation attorney, is on the airline team this time. Patricia A. Goldman, a former congressional aide who participated in NTSB investigations of railroad accidents in New York City and Philadephia, is working the Metro crash.

The teams follow similar procedures in interviewing witnesses and gathering evidence. The railroad team will get most of its information from Metro passengers, the subway operator and Metro officials.

Airline teams concentrate on the structure of the airplane, the electrical and hydraulic systems, the engines, the history of the flight from takeoff to the crash and the pilot's intentions.

They also look at the air traffic control operations, weather, human factors, including why people died, witnesses' accounts of the crash and maintenance records of the airplane.

The team can call on other federal agencies or airline industry experts for help. So far, the NTSB team investigating Wednesday's crash has asked for help from Air Florida, the Federal Aviation Administration, Pratt & Whitney (the company that made the jet engines) and Boeing, manufacturer of the 737 that crashed.

Because the crew of the airplane died in the crash, the aviation team is concentrating on finding two vital instruments, a cockpit voice recorder and flight data recorders, kept in the tail of the aircraft.

Even though the tail section sank in the Potomac, NTSB investigators say they believe the instruments will work if they can be found. Both instruments are encased in fireproof and waterproof high-impact containers.

It will probably be six to eight months before the team finishes its investigation of the airplane crash, an NTSB spokesman said. The subway accident should take less time to investigate.

The airplane crash team will hold nightly meetings at its command center in the Twin Bridges Marriott Hotel to discuss what each investigator has found. Once the team decides it has done its field work, it will return to NTSB headquarters for extensive laboratory testing of various instruments and parts of the plane. Eventually, both teams should be able to explain what happened.

Kapustin was asked in a 1976 interview how he and other investigators coped with being called to the scenes of so many tragedies.

The team, he said, had to look beyond the accident. Rather than dwelling on the "if only's" that might have prevented it, he said, they focus on how they can try to ensure that it won't happen again.