At least five residents and police officers yesterday morning reported what they described as one or more jets flying unusually low as the aircraft moved down the Potomac River toward National Airport.

A Federal Aviation Administration official speculated, however, that low-lying clouds made the jets appear to be flying at a lower altitude than they actually were. The official suggested that low clouds can distort viewers' depth perceptions. "They see the aircraft against the clouds . . . the aircraft looks a lot more ominous. It looks a lot larger," he said.

The FAA official said that all jets landing at the time mentioned in the reports made normal instrument approaches under an 800-foot cloud ceiling. Supervisors in the air-traffic-control tower at National said airport radar showed that all planes landing in the period indicated were at the right altitude and on course, the official said.

An Arlington County police car patrolling during morning rush-hour radioed to headquarters that one or more planes "seemed to be in the approach awfully low in Rosslyn" and asked that the FAA be notified, a police spokesman said.

On the Washington side of the Potomac, a D.C. police officer made a similar observation over police radio yesterday morning.

A spokesman for the National Transportation Safety Board said that a woman had called to say that a jet had passed unusually close to her building in Rosslyn. Three or four people--one of whom was a woman--called the control tower at National directly, an FAA official said.

The reports came five months after office workers in Rosslyn reported that a Piedmont Airlines 737 approaching National Airport under low clouds had passed unusually close to the USA Today building. That incident renewed debate among aviation groups over whether an airport can operate safely close to a downtown area.

The safety board, following an investigation in which the plane's flight recorder was read out, concluded in March that the plane had probably been too low and off course and recommended that the FAA shift one of the airport's instrument flight paths to keep planes farther from the Rosslyn high-rises.

The FAA has not yet responded formally to the findings and recommendations, but has said that the approach paths from the north--one of which the planes were using yesterday morning--are safe and fully meet federal standards.

Because of low clouds, the jets were using a common instrument approach in which they ride an electronic beam that roughly follows the Potomac's course. As a plane passes Rosslyn, it is meant to be flying at an altitude of about 720 feet. If the crew cannot see the ground and fly visually at that altitude, the plane is required to go around and try to approach again.