Two jetliners, speeding toward each other at about 500 mph and carrying a total of 208 people came within 200 to 300 feet of colliding over North Carolina Wednesday evening, the captain of one plane has reported to the Federal Aviation Administraion.

The incident occurred shortly after an air traffic control radar failure in Leesburg in suburban Virginia.

The pilot of an Air Florida Boeing 737 took an evasive turn to the left to avoid the other aircraft, a Delta Airlines Lockheed £1011, officials said yesterday. The Delta pilot apparently spotted the Air Florida plane first and turned on his landing lights to give warning.

"Our pilot said the other plane was about 10 to 12 miles in front of him when he spotted him and turned on his lights," Delta spokesman Bill Berry said, "but the planes were much closer (when they cleared each other)."

The pilot of the Air Florida plane told the FAA and his company officials that the planes passed within 200 to 300 feet of each other. At the altitude where the incident occurred -- 29,000 feet -- airplanes are supposed to be 1,000 feet apart vertically and five miles apart laterally.

The planes were at top cruising speed and headed directly toward each other. Delta Flight 1061, with 115 people on board was flying nonstop from New York to Fort Lauderdale. Air Florida Flight 721, with 93 people on board, was en route from Miami to New York. The incident occured about 7 p.m. Wednesday about 20 miles northeast of Wilmington, N.C.

The Air Florida pilot, Wallace Ruck, officially complained to the FAA and filed what is called a "near miss report."

The agency operates the air traffic control system, including the giant regional facility at Leesburg that is responsible for most East Coast traffic between the North Carolina-South Carolina border north to the Maryland-Pennsylvania border and west to the Blue Ridge.

The FAA's air traffic service is formally investigating the incident, which it calls a "systems error."

Angelo Viselli, chief of the FAA Air Route Traffic Control Center at Leesburg, said in an interview yesterday that the incident occurred shortly after full radar operation had been restored at Leesburg. In the process, for reasons not yet understood, the radar "lost" the Air Florida plane.

The huge en route rada system is entirely computerized, and the Leesburg sceens identify for controllers each airplane, its altitude and speed. However, when the computer "goes down," controllers are forced to use World War II-era back-up equipment. They have to scramble to reidentify the tiny dots on their screens and to insure that safe distances are maintained between aircraft.

The Leesburg computer failed for six minutes Wednesday, an unusual "significant" failure, according to Viselli. As controllers scrambled to relocate all the airplanes in their sectors at one of the peak flying hours of the day, two new things happened:

The Air Florida plane, curising at 29,000 feet, entered the Leesburg airspace from airspace controlled in Jacksonville. Normally, the Jacksonville computer would "talk" to the Leesburg computer and a "handoff" would be executed automatically. This time, however, a Jacksonville controller had to call a Leesburg controller and tell him the Air Florida plane was his.

The Delta captain, Joe Lacey, was flying along at 31,000 feet and found the going a little bumpy. He requested, and was granted, permission from Leesburg to descend to 28,000 feet.

The computer then came back on and most of the airplanes were reidentified. For some reason, and according to FAA officials the technical answer could rest in either the cockpit of the Air Florida flight or the Leesburg control room, the identifying data did not reappear for Air Florida.

After the incident occurred the Air Florida pilot immediately radioed Leesburg and complained.

According to the FAA, there were 586 "systems errors" reported from January through August this year, many of them far less serious than the Air Florida-Delta incident.