The president of the Montgomery County Council has accused the Federal Aviation Administration of permitting violations of federal rules limiting the hourly number of takeoffs and landings at National Airport to the point where safety is compromised.

In a letter to FAA Administrator Donald D. Engen released yesterday, council President William E. Hanna Jr. said an analysis of daily flight operations in December showed that scheduled commercial and commuter flights exceed their hourly caps of 37 and 11, respectively.

In some cases, he said, the FAA's own count of scheduled flights shows that as many as 50 jet airliners and 19 commuter flights arrive or depart each hour at the FAA-operated airport. Even with good weather conditions, Hanna wrote, "this number and frequency at an airport with only one main runway, which itself does not meet FAA standards, pushes the limits of safety . . . . "

The Feb. 27 letter to Engen is the second expressing concern over violations of FAA rules limiting flights at National and was sent because Engen's reply to the first letter in November wasn't "responsive enough," Hanna said. The first letter was written by council member Michael Gudis, who was council president at the time.

"The takeoff patterns come over a considerable part of Montgomery County," Hanna said in an interview, "and Montgomery County and our citizens are outraged by the noise and potential for safety [problems]. We feel the airlines are not being monitored properly," and the FAA is violating its own regulations on the hourly caps.

William Moran, chairman of the Prince George's County Advisory Board on National Airport, said Hanna's letter was particularly timely in view of a federal report that air traffic controllers nationwide are overworked. Moran's advisory board works closely with Montgomery officials.

The General Accounting Office report released Thursday said it would be "prudent" to limit growth in air traffic before the system loses its "proper margin of safety."

FAA spokesman Dave Hess said Engen would not comment on the most recent letter until he has had a chance to study it.

But, Hess said, "if people here felt there were unsafe practices, they wouldn't be permitted." He added that he did not believe extra operations beyond those scheduled in a given hour constitute "a flagrant thing."

Hess said it is not unusual for airports to exceed their allotted hourly caps on scheduled flights because such factors as poor weather or mechanical failures can lead to more or fewer arrivals and departures per hour.

He said daily totals for regularly scheduled aircraft operations at National usually even out to 37 operations an hour for jetliners and 11 for commuter planes.