The Federal Aviation Administration held a public meeting last night on National Airport, one of the most controversial facilities in the Washington area, but only nine citizens showed up.

The hour-long session was marked by long silences when the call for questions went out. The nine in the audience were outnumbered almost 2 to 1 by FAA staff on hand to help out with detailed answers.

"Either there's a lack of interest or someone didn't get the word," said Henry L. Mahns, manager of the planning branch for the FAA's metropolitan Washington airports, adding that dozens of letters and press releases had been sent out to traditionally interested parties besides the required legal notices. In addition, the meeting was held in the Marriott Crystal Gateway Hotel in Crystal City, an area close by neighborhoods that have supplied some of the criticism of airport noise and crowding.

Staff members of the FAA, which owns and operates National and Dulles International airports, expressed surprise that the public "informational session" did not bring out the usual civic groups that use such forums to lobby for closing National and rerouting traffic to Dulles and which have strong views on the proposed "scatter plan" for arrivals and departures of aircraft.

But the session was only the first of four FAA officials expect to have before the year's end on a master plan for the long range modernization of the 42-year-old airport's facilities.

In February the FAA awarded a $1.1 million contract to the consulting firm of Howard, Needles, Tammen & Bergendoff, whose representatives last night outlined subjects they will study such as car and air traffic congestion, noise abatement, physical appearance of airline terminals and improved connection--but not realignment--between the Metro rail stop at National and the airport's terminal.

The FAA's Mahns said the study will be based on the current policy to cap the annual number of passengers using National at 16 million. But, the study, which will focus on facility needs by the year 2000, will also include projected needs for a 12 million passenger ceiling.

"We're looking at the low figure simply because we don't know where the policy could end up," Mahns said. Secretary of Transportation Elizabeth Hanford Dole has suggested lowering the annual passenger flow to 14.8 million.