If Friday had not been so unusually busy. commercial operations at Washington National Airport would have shut down by about 10 p.m.

But flights from Chicago, delayed by bad weather and filled with holiday travelers taking advantage of newly lowered airfares, were still arriving at 10:45 p.m. when the threat came in "Bomb on Flight 59," the caller told the airline clerk.

By the time Piedmont Flight 59. which was supposed to have been a direct flight from Newark to Richmond, touched down, an Army bomb squad was ready to board it in a remote airport area called, with grim humor, the penalty box.

No bomb was found aboard Flight 59. Its 68 passengers and crew of four continued on to Richmond two hours after their unscheduled visit to Washington National. Patrick C. Hawes, the Federal Aviation Administration operations oficer in charge of handling the bomb threat, called the day "routine."

This is Washington National Airport, a portal through which more than 14 million travelers pass a year, 710 acres bursting at the seams with a parade of congressmen, confused tourists, occasional diplomats, anxious lobbyists and sundry bureaucrats. If Washington sometimes claims the chauvinistic title of capital of the world, the airport is its front door. Call it confusing. Color it fun.

An official for Security 76, a company that screens passengers before they are allowed to board ilights, was musing about the people he has seen.

"Wouldn't you consider a drunk riding through the belt of an X-ray machine a little odd?" he asked. "He put his suitcase down on the belt and then just followed it through."

"Some people try to put babies through the X-ray machines," his colleague said, tapping her head lightly. "People can be funny up here."

There was, for instance, the man who refused to open his briefcase for a search. When security guards insisted, he simply left it behind. The airport police later found that it contained $40,000 in cash. The man simply vanished and was never identified.

There was also the foreign diplomat who came through -- or tried to -- wearing three handguns. He was disarmed. And the man who arrived wearing little more than a hat and coat -- and was arrested, an official report said, for "creating a disturbance." And, of course, the fellow who wanted to bring a four-foot lizard aboard as hand baggage. Request denied. The lizard rode in the baggage compartment with the other pets.

The 710 acres that comprise Washington National Airport would fit inside the terminal areas of other airports such as John F. Kennedy in New York. Yet, on an average day, 38,000 travelers pass through it.

"It's a postage-stamp sized airport," says Jamison Hurst, deputy chief of the control tower. "It's like a small city." says Everett S. Lindley, an FAA operations officer. It is the nation's ninth largest commercial airport, and on the last Friday before the New Year it was brimming with people headed for 1979. In its parking lots, as usual, a "reutine" day meant chaos.

Outside the main terminal, Officer Louis Moody of the Airport Police was dancing a desperate bailet in the small traffic circle, waving and bouncing as he urged on a daily traffic flow that included 8,000 taxis and countless other cars.

"The parking lots full sir, you'll have to move on. No, sir, no, you'll have to move on."

"There's a problem with parking out here," he explained. "People don't understand that if I let them wait, I have to let everybody else wait." Then he returned to his dance.

"No, ma'm, I'm sorry, you'll have to move on." Her response was inaudible from behind the car window, but the word formed by her lips was not polite.

"Everybody's going to be here for just 90 seconds." Hugh Riddle Jr., the airport manager, said sarcastically. "Aunt Minnie comes for Christmas from Dubugue and the whole family wants to meet her at the gate. So they drop anchor at the circle, and the plane's a half hour late. Then they complain when the car is towed away."

Last week was unusually busy at Washington National, Riddle said. The week after Christmas is normally quiet, he said, but the recently lowered airfares has the terminals humming.

"The sunrise at the airport is really beautiful." said Candace Erannan, who sets out at the wheel of a courtesy bus at 6 a.m. each workday on an eight-hour, 70-mile odyssey, circling through the airport parking lots.

"You met a lot of interesting people." she said. Last Thursday, for example, she saw a man in a gorilla suit."But he didn't get on the bus, so I don't know what he was doing."

"Actually, there were three of them." said Joe Maurer, an operations officer for the FAA, which runs the airport. "It happens every now and then when people want to greet their friends with a little surprise. Usually, they have musical instruments."

"You should have been here the time the monkeys broke loose." said John Ogden, the chief operations officer. The monkeys escaped from a baggage crate. Eventually they were recaptured, but not before prancing around the terminal to the delight of several television crews.

Monkeys apparently enjoy airports. People sometimes don't. "Most people are scared of an airport because it's an alien environment." said Judy Lewis, a ticketing agent. "They don't think, they just react."

According to Lewis, some react badly, too. She recalled the man on his way to the ticket counter who passed a nearby post office box, mailed his ticket and absent-mindedly presentled a handful of letters at the counter. A postal service employe managed to retrieve the ticket before the flight left.

O. G. Purnell, who works in the Eastern Air Lines lost and found, admists he doesn't have the world's happiest job. People seldom bring him good news, and most who seek him out have lost something aboard a plane.

"One man lost his shoes." he recalled. "He came in barefoot. He just forgot to put them on when he left the aircraft. You sit here and you say you'll never believe it." Someone else left a set of false teeth on board. But mostly, it is lost baggage.

Still, some of the baggage people travel with is surprising. Theodore Hughey, a skycap for American Airlines, said he has a number of passengers who arrive at the airport with automobile tires. "The people that live in Chicago, they'll come and buy them here because they're cheaper here, I guess," he said.

But Hughey, who attributes his seemingly unshakable good humor to the fact he is a born-again Christian, said the luggage doesn't bother him if the passengers don't. Among those who try to pull rank, he said, is the occasional congressman.

"First thing I tell them is, 'You're the lawmaker, not the lawbreaker.' I'm not going to drop one passenger just because another is a congressman."

Airport traffic can also be a reliable political barometer. "You can tell when a big bill is coming up," said deputy control tower chief Jamison Hurst, who explained that the nationwide interest in a major piece of legislation can increase the daily level of takeoffs and landings from the normal 800 to 1,100 with private planes making up the difference.

in the darkened radar room inside the tower, where Hurst's air traffic controllers stared warily at little green blips on rada screens, it was apparent Congress was not in session.

"Cardinal five eighty-three," the chatter went. "Squawk one-two one-two. What is your altitude request? One-six yankee contact Baltimore. Traffic on your right, 2 o'clock, four miles." Three flights landed, one took off, then the sky was empty for a while.

And then Eastern Flight 1531 showed up. Among its living cargo was an elderly couple in large fur coats, a couple of basketball players, a family in cowboy hats and a human kidney packed in a $6,000-machine that kept it alive. The kidney was on its way to a transplant at Walter Reed Hospital.

"This airport touches people's lives," said David McRonald, the airline official in charge of getting the kidney safely off the plane. CAPTION: Picture 1, Taxis await their turn to get to passenger pickup area at National Airport, by Tom Allen-The Washington Post; Picture 2, The main concourse at Washington National Airport's main terminal was crowded with visitors Friday. By Tom Allen-The Washington Post; Picture 3, Theodore Hughey, a skycap at National Airport, wheds passengers' luggage in to an airline check-in counter. By James A. Parcell -- The Washington Post; Picture 4, Controllers at the National Airport control towar direct plances leaving or landing at the airport. By James A. Parcell -- The Washington Post