A FRIEND who works in advertising in New York tells me that all parks fall into two categories: those suitable as backgrounds for menthol cigarette ads and those unsuitable.

Gravelly Point, 65 acres of pocket park sandwiched between George Washington Parkway and the Potomac, falls (loudly) into the second category. It's a great place to launch a boat, start a jog or a bike trip along the Mount Vernon Trail, kick a ball or enjoy a picnic. But don't expect peace and quiet, for Gravelly Point is just off the end of National Airport's busiest street, Runway 18-36.

Nearly a thousand aircraft a day land or take off from National, and there is probably no public park in the country closer to the action at a major airport than Gravelly Point. On a clear day, it seems like you could reach up and scratch the tires on a DC-9 thundering in over your head. (You couldn't, of course. It's doubtful that they ever come closer than 75 or 100 feet when making their final approach. But as that speck on the horizon quickly becomes a full-sized commuter jet headed right at you and the ocean whisper of its engines becomes a whine, then a rumble and finally a dragon roar that shakes the organs in your chest, you're not likely to wish it was any lower.)

On warm days the planes appear to melt as they land in the image-bending thermal waves and fuel fumes on the runway. Two puffs of gray smoke as the tires touch down let you know that another jet has made it in safely. The ballet is punctuated by blasts from air cannons mounted at either end of the runway to scare away birds so they don't get sucked into engines.

Planes always take off and land into the wind. When it's from the north, they take off over Gravelly Point -- an even louder experience -- and touch down on the far end of the runway. When the wind's from the south, they come in over the park and take off downriver. It's more dramatic when the planes make their approaches over the park, as they come in lower. A departing aircraft gains altitude very quickly. Incidentally, pilots never see the people watching from Gravelly Point, according to an airport operations officer at National; they're too busy watching the runway and their instruments.

The daily drama of airport operations attracts all kinds of people: picnicking tourists, bureaucrats on their lunch hours, cab drivers taking a break from the gridlock at the airport, and an assortment of people who simply pick a good spot in the parking lot and settle in for a few minutes or a couple of hours of Airport, the Real Thing.

There's a small group of regulars who come out with lawnchairs and VHF radios, sit as close to the fence as they can and listen in on the pilots and tower. "There was this one guy last week in a corporate jet," says Arno Frost, who served in the Air Force and comes out four or five times a week, "and I saw him coming in so low I started to take my chair and run. Man, I thought he was going for a swim. He made it, though. But the best time to come out is in bad weather. That's when it really gets interesting."

(A Realistic Jetstream AM-VHF radio is available at Radio Shack for around $10 and is all you need to get started. The airport tower is 119.1 on VHF; ground control is 121.7 VHF. The Park Service is reportedly planning to put up a wayside exhibit that would include a radio monitor and a sign identifying the most common aircraft.)

Even on a clear day, there are a number of "go-arounds," instances in which an incoming plane arrives before another has cleared the area, and is told by the tower to circle for another approach.

One of the regulars hands me his binoculars and has me train them on a commuter jet with two huge engines preparing to take off.

"Hear that?" he asks.

"Hear what?"

"Exactly. That's a 757. A DC-9 at full throttle will blow your ears off. But that 757 just whispers." The 757 (when equipped with special Rolls-Royce engines) is the only large jet quiet enough to be exempt from National's 10 p.m. curfew on planes above a certainnoise level. The MD-80 is allowed to land any time, because its incoming roar is below 72 decibels; but it can't take off between 10 p.m. and 7 a.m. because its outgoing racket's above 85 db.

On a warm Saturday afternoon, surrounded by picnickers, joggers, lovers, bicyclists and fellow planewatchers, Frost dutifully lists for a newcomer the attractions of Gravelly Point. "There's the planes, the river, my friends, it gets me out of the house, plus there's usually a nice breeze out here."

"Now tell him the real reason," prompts a buddy in a Boeing baseball cap.

"Okay, okay. It's a great girlwatching spot," he says.

One of the pastimes of the aircraft- watchers is identifying the changing owners of commuter jets under deregulation. One points out a Northwest DC-9 and explains that since the registration number on the side ends in NC, he knows that it used to belong to North Central, which was bought out by Northwest. Its solid red tail is part of the Northwest color scheme, but it still lacks Northwest's blue fuselage stripe. "They'll probably get around to putting it on the next time it goes in for an overhaul," he says.

Gravelly Point was created in the early 1960s by dumping dirt left over from federal construction projects, including the Civil Service Commission, now the Office of Personnel Management. The National Park Service, which oversees the park, estimates that 1.3 million people visited it last year, making it one of the busiest on the parkway.

While the big attraction is the planes, the park's a magnet for a variety of people with other interests. The free boat ramp is one of the best in the area and wide enough to accommodate three or four boats at a time. There is nearly always somebody working on the tricky physics of backing a car the opposite way the trailer is supposed to go. On weekends, by 9 in the morning the parking lot contains a good number of empty boat trailers, spindly, skeletal contraptions not unlike the bones of the bass many of the boats are stalking in the river's flotillas of hydrilla. There are also a good number of shorebound fishermen sitting on overturned buckets trying to fool the river's ubiquitous catfish.

Then there are the two soccer and football fields. On Sundays, there's usually a series of three soccer games held by the Guatemalan Soccer League, 13 teams whose players are mostly from Central or South America. The friends, families and acquaintances of the players, sometimes as many as 600 of them, come out to make a day of it, setting up tables and barbeques. The season runs March through June, then picks up again from the end of August through late December. "It's sort of a cultural thing for us," says league founder Jay Alberto Morales. "It's a chance to get together as a community." The Northern Virginia Rugby Club also uses the fields.

The park lies astride one of the busiest sections of the nearly 17-mile Mount Vernon Trail, which stretches from Mount Vernon to the Lincoln Memorial. An unending stream of bicyclists in stylish spandex or old sweats, on Italian racers and one-speed clunkers, rolls down the path, as do joggers, hikers and strollers. Gravelly Point is a two-mile ride south from the Lincoln Memorial, about five miles north of Alexandria and seven miles north of Dyke Marsh, a 240-acre wetland typical of the Potomac estuary and a favorite of area birders. (Cyclists, be warned: The Park Police have announced that they may begin giving tickets to riders who ignore stop signs or exceed the 15 mph speed limit. Fines can go as high as $50. Traffic on the path is increasing, as are accidents. That weirdo in the bushes with a hairdryer may actually be a Park Police officer with a radar gun.)

Besides airplanes, Gravelly Point may also be the vantage point from which to see more other kinds of transportation than any other spot in the area. There are bikes, cars, boats (one day I watched a guy drive a little sort of hovercraft right off his trailer, over the grass and into the water), AmTrak trains crossing Long Bridge, and Metro trains crossing the river on their own bridge. All that's missing are submarines.

But it's late on a Saturday night, when the parking lot is half full, with more people still coming in, the boat ramp's still crowded and planes are hurtling into the carnival of blue, red and white lights at National, that you get to see Gravelly Point for what it truly is -- a world-class place to hang out. GETTING THERE --

From the George Washington Parkway north, turn right at the first exit after National Airport. Ifgoing south on the parkway, take the National Airport exit, stay left and follow the signs back to Washington to get on the parkway headed north.