Air traffic at National Airport was snarled for close to an hour yesterday morning after a broken landing gear immobilized a private plane at a key runway intersection, forcing closure of two of the airport's three runways.

Three arriving airplanes were diverted to Richmond and Baltimore-Washington International airports and others circled as maintenance crews worked to remove the crippled plane, a four-seat, single-engine Beech Bonanza, Federal Aviation Administration officials said.

At New York area airports, passengers bound for National found their flights delayed as the FAA's Central Flow facility in Washington, which monitors air traffic nationwide, held planes on the ground.

FAA officials said some flights scheduled into National were delayed up to 30 minutes. Traffic began returning to normal shortly before 10 a.m. after the crippled plane was towed off the field for repairs, FAA officials said.

During the closure, planes continued to land and take off on the single open runway, which is National's shortest at 4,724 feet and does not normally take arriving jets because its approach path passes over heavily populated areas of Alexandria.

The incident began about 8:50 a.m. when the light plane landed from the north on National's 6,870-foot main runway, known as Runway 18/36, and began taxiing toward the terminal.

The nose gear collapsed as the plane crossed the intersection with another National runway, the 5,210-foot Runway 15/33, said airport spokesman David Hess.

The only person aboard, identified as James Pezza of Fairfield, Conn., was not hurt, Hess said. The FAA has not determined the cause of the accident, according to Hess.

National often logs 75 to 80 takeoffs and landings an hour during busy weekday mornings. Yesterday, with two runways closed, 43 planes, including 16 jets, took off or landed on the single runway, according to tower chief Harry Hubbard.

Three planes elected to divert to BWI and Richmond rather than land on the short runway, Hubbard said.

Jetliners heavily laden with fuel and passengers are not allowed to use the short runway because of concern they will not be able to stop in the distance provided. Pilots of jets that meet the weight standards for takeoff often request the short runway, because its departure path takes them up the Anacostia River and cuts up to 10 minutes off the flight to New York.

The runway is not normally used for landings because planes approaching it pass over densely populated areas of Alexandria. Noise control regulations in force at the airport since the 1960s generally require that jets follow the Potomac River.