Although it has a little-publicized number that's almost impossible to find in the telephone book, the phone at Washington National Airport's Sound Complaint Center can get as busy as the airport it serves.

For example, it rang incessantly one recent Sunday night after a Concorde departing from Dulles flew unusually low over residential areas. Then there are days that the phone remains practically silent.

"We get calls on every kind of noise imaginable - from dogs barking to motorcycle noise to subway construction," said John Ogden, who answers the 557-2081 Sound Complaint Center line when he is on duty as the airport operations officer. When people have complaints about noise pollution, they seem to have no trouble locating the center number, he said.

"When you're called a Sound Complaint Center, people just feel you're the proper place to call," he shrugged.

The Sound Complaint Center isn't a center at all. It is a special phone line that rings in the airport operations office 365 days a year.

The "center" was established in 1966, when jets first came to National Airport, said airport manager Hugh Riddle. When Riddle came to National Airport 12 years ago, his full-time job was to draft thousands of answers each week to noise complaints.

The number of complaints has decreased drastically, with the center usually receiving anywhere from one to about 25 calls a day, Riddle said.

Much of the improvement is due to improved cockpit techniques and recent noise abatement procedures, which call for planes taking off and landing in patterns that follow the Potomac River, he said. People also have gotten used to jet noise, or they tend to feel calling doesn't help and give up or move away, Riddle said.

But with 325,000 take-offs and landings a year at National Airport, the Sound Complaint number is never totally ignored.

"When the weather is bad, with a low ceiling and visibility, you can expect the phone to ring," said operations officer Bernard McGinnis. Under these conditions, pilots must rely on their instruments to fly and may be forced to fly over land. This results in jet noise over residential areas, which usually prompts complaint calls.

"Most people are generally reasonable," said McGinnis, who explains to callers why bad weather means increased noise. "But some get so irate they can't even carry on a conversation."

Each phone call and letter that comes into the Sound Complaint Center is recorded and answered, Riddle said. Accumulated records supply airport officials with a data bank of high noise areas. Calling the Sound Complaint Center also gives persons who live along the flight paths a place to let off steam.

Calls are seasonal and increase during the "open window seasons" of fall and spring. During these times people are more aware of airplane noise than they are when their homes are tightly sealed against the heat of summer or cold of winter.

Calls have come from as far away as San Francisco, added Officer Ogden, who said he regularly gets letters from anti-airport people suggesting alternative uses for the land, such as turning it into a large volleyball field or a marina.

"Some people are just inordinately afraid of airplanes," said Ogden, who calls this phobia the Chicken Little Syndrome. "Hearing an airplane engenders a fear within them.

"But most people have a logical basis for calling. The sound is intrusive, and they don't have a good understanding of the difference between visual flying and instrument flying."

Other than following the noise abatement procedures and attempting to keep take-offs and landings over the river, there isn't any way to completey stop airplane noise, Ogden said. "There's just no such thing as a silent airplane."