In most communities, the roar of planes overhead would be considered a nuisance. But in Manassas, it is music to the ears of city officials and airport manager R.H. Moore.

"Those planes are the key to making this area a center of corporate activity," Moore said of the air traffic at the city's 18-year-old municipal airport.

Last week, Prince William County supervisors agreed, voting to extend one of the Manassas airport's two runways by 1,700 feet in an effort to lure corporate passenger jets from nearby National and Dulles International airports.

The move was lauded by local Federal Aviation Administration officials, who say there is a shortage of airport space for private jets and airplanes in the metropolitan area.

"Most towns treat their airports with indifference at best," said William A. Whittle, manager of the FAA's Washington Airports District Office in Falls Church. "Manassas is a rarity in that it has been very aggressive about promoting their airport. They've done a beautiful job of it."

Whittle said other local airports, such as the Woodbridge Airport in Prince William County and Hyde Field in Clinton, are being hemmed in by residential development and may not last the decade.

"That's why it's so important that Manassas is willing to take on more of the load," he said.

The extended runway will allow larger passenger planes and private jets to land at Harry P. Davis Field and will increase air traffic in Manassas by 20 percent--to about 75 takeoffs and landings a day--when it is completed in fall 1984, Moore said.

The airport, which does not have air traffic controllers in attendence, logged 200,000 plane operations last year.

Federal aviation grants will pay 90 percent of the $5.6 million tab for the extension, Whittle said, and state grants will pay about 7 percent. That will leave Manassas with a bill of about $200,000.

Although the Manassas airport does not charge takeoff or landing fees, city officials hope those who use the airport will buy gas there and shop at local stores. Most of the planes now landing at the airport are owned by businesses and are used to haul freight or transport executives. There is also a small commercial passenger line, Colgan Airways, owned by State Sen. Charles J. Colgan (D-Prince William).

The airport, on Piper Lane, about 35 miles south of the District, is owned by Prince William County but will be turned over to the City of Manassas if a trade agreement between the two jurisdictions is approved by the courts this summer.

It is on 540 acres just outside the city limits but far from residential development, so there has been no vocal opposition to the expansion plans.

Moore said both Prince William and Manassas officials hope the expanded airport will help convince corporations and businesses to settle in their area.

At International Business Machine Corp.'s office in Manassas, company spokesman Norm Koestler said a good local airport can be attractive to corporate executives looking for a potential headquarters site.

"Manassas has been very convenient for us," he said. "I imagine others might find it also."

Although Moore said he believes some private jet traffic will be routed from Dulles and National when the runway is completed, airport officials said they doubt the new runway will affect the two major airports because they already limit the number of private planes using their runways.

"We welcome them," National spokesman Dave Hess said of the Manassas plans. "But we allow 12 general aviation landings private planes and small jets an hour, and I don't think that level would drop. On clear days we can handle more."

He said Dulles also limits the number of general aviation aircraft allowed every hour and has been able to handle the demand.

"Yet we still need more general aviation space in the area," Hess said. "It is a growing field. There seem to be more private jets coming out of this area every year."

Whittle agreed, saying the FAA is studying the possiblity of using an Army airfield at Fort Belvoir for commercial air traffic.

"We've studied this ad nauseam over the last decade because the military is not happy with the idea," he said. "But every year air space in this area gets a little tighter. Manassas is the exception, not the rule here. Most small airports are getting squeezed."

Despite construction to expand one of the runways, planes will still be able to take off and land at the municipal airport. And in his office in Manassas City Hall, R.H. Moore already is poring over plans to build another terminal along the second runway.