The Arlington County Board reaffirmed its opposition last night to the closing of National Airport, but agreed to endorse a lower ceiling on the annual number of passengers there.

The board's action came in response to citizen concerns about noise and safety risks involved in airport flights and to a proposal by the National Capital Planning Commission, the federal planning agency for the Metropolitan area, to close the Arlington-based, federally owned airport, in 15 to 20 years. The NCPC has scheduled a public hearing on its proposal for Feb. 3 and will forward its recommendations to the U.S. Department of Transportation and the Federal Aviation Administration.

The board agreed, 4 to 1, to a motion from John G. Milliken that it endorse a plan to reduce the currently approved ceiling of 16 million passengers annually to 14 million, a figure close to the 14.2 million annual passenger traffic today.

Walter L. Frankland dissented, arguing that the board should wait until it appoints the citizen study committee that it agreed to create last night. The committee is to study the economic, health and environmental impact of the airport, which is adjacent to Crystal City, a high-rise complex of hotels, office buildings and retail stores.

The board's opposition to the NCPC's plan is its second battle with a federal agency in a month. Earlier, the board fought a Navy plan, endorsed by NCPC, to shift 18,000 employes, most of whom work in Crystal City, to the Navy Yard in Washington. The Navy said last week it was abandoning that plan.

"National airport is an important part of Arlington County, but clearly we want limitations on operations there . . . . " Milliken said. "I think we want to send the message that the board wants to exert pressure on a downward basis . . . and that we shouldn't be encouraging them to expand."