Two Delta Air Lines jets flew dangerously close to each other over Front Royal Sunday night because of a possible air traffic control error, Federal Aviation Administration officials confirmed yesterday.

The two Boeing 727 aircraft, carrying a total of 161 persons, came within 1.3 miles at the same altitude, 35,000 feet. Airplanes cruising at that altitude are supposed to be at least five miles apart

The error was abetted by a problem in the FAA's computer system, which forced controllers to place both planes in a holding pattern. Holding patterns, where planes fly in circles while awaiting permission to proceed, are among the most complex air traffic control maneuvers and have been the source of multiple controller errors.

Charles R. Reavis, manager of the FAA's Air Route Traffic Control Center at Leesburg, said the 8:30 p.m. incident was not considered a near collision. "The controller had control of both aircraft . . . they were just too close," he said.

"It appears to be a controller mistake," Reavis said. "It was not Delta's fault."

Delta, which has an outstanding reputation in the aviation industry, has been plagued in recent weeks with a series of startling safety-related incidents. The most dramatic occurred over the Atlantic Ocean when Delta and Continental Airlines jumbo jets came with a few feet of each other after the Delta jet strayed 60 miles off course.

A Delta spokesman had no comment on the incident.

The FAA is still investigating the Front Royal incident, which occurred as the two planes turned away from each other, Reavis said. In addition to controller error, other causes could be pilot error, communications problems or mechanical malfunctions, he said.

However, he said, it appeared that a controller directed the two aircraft into holding patterns that were too close, he said. Both planes -- Delta Flight 487 from Boston and Delta Flight 589 from Philadelphia -- were headed for Dallas.

The Leesburg center led the nation in controller errors last year, with 83. The center has recorded 53 this year, compared with 41 at this time last year, Reavis said.

Nationally, the 20 air route traffic control centers, which handle flights after they have left the control of local airport towers, recorded 654 controller errors in the first six months of this year, about half of the 1,207 total for last year, an FAA spokesman said.

An unidentified Leesburg controller directed the two Delta flights into holding patterns because of unspecified computer problems at the FAA's regional air traffic control center in Atlanta, Reavis said.

Both flights were scheduled to traverse Northern Virginia airspace, then be "handed off" by controllers at Leesburg to controllers at the Atlanta air route center. The Atlanta center asked Leesburg to hold the flights temporarily because of the computer problems. The air traffic computers are used to generate symbols portraying airplane movements on controllers' radar screens.

The Atlanta center, like Leesburg, is due to receive new computers as part of a $12.2 billion, 12-year Transportation Department modernization program.

Leesburg expects to receive faster, higher-capacity computers this fall. It has suffered several computer outages during the past six months.