THE FUN OF FLYING is secondary, in my opinion, to the fun of watching flying. Luckily for people like us, there are others for whom flying is the greatest fun in the world. Several of those people can be found every Sunday from May through October flying antique airplnes above the fields of rural Virginia near Warrenton. Those magnificent men in their flying machines are so frightfully keen that they can take their colorful World War II airplanes through loop-the-loops, cut ribbons with their planes' wings, pop balloons with their propellers, and carry wingwalkers upside down.

The Flying Circus in Bealeton is one of the country's two remaining old-fashioned barnstorming shows (the other, in Poughkeepsie, N.Y., features World War I planes). This weekend, the air show will be held both Saturday and Sunday along with the 14th annual Hot Air Balloon Festival, featuring 40 balloons.

If you've never seen a meticulously restored biplane that wasn't hanging from wires, then the planes themselves are a good reason to see the Flying Circus. Aviation buffs will appreciate some of the names: a 1940 De Havilland Tiger Moth, two 1929 Fleets, a 1941 Stearman, a 1940 Waco. And all will be thrilled when six planes take off in formation to begin the 90-minute show.

The stunts may not be dangerous, but some call for an extraordinary amount of skill and precision. The only reason they're not dangerous is because the pilots have been doing them for years. When a long-bearded old farmer named Charlie Kulp steps up to claim his free ride and then steals the airplane, he quickly proves he's no ordinary farmer. Charlie's maneuvers make it look as though both he and his plane have been loaded with high-proof, low-octane fuel. I got a little dizzy just watching.

The announcer, who keeps up a lively commentary, the planes, the pilots and the history of aviation will tell you that many of the stunts were designed as training exercises for the military.

Two or three of the pilots are still in their 20s, and between the comedy acts they perform breathtaking aerobatics. An aviation maxim, by the way, maintains that there are old pilots and there are bold pilots, but there are no old, bold pilots. Anyway, one of these bold pilots will take a Pitt Special roaring down the runway, flop it over a few times, come screaming low over the airfield at 200 miles per hour, shoot straight up in the sky several hundred feet, hang there vertically for several fat seconds. then dive down to just above the ground, carve out the shape of the hugest, meanest roller coaster known to man, rip hell out of the air a few more times, and then, just as you're begging him to come down so you can relax, he comes tearing out of nowhere one more time in an attitude that makes it clear, in case there was ever any doubt, the poor boy never did learn up from down.

As for the old pilots, many of them flew in the war and for commercial airlines, and they've survived long enough to realize that humor is the better part of valor. In seventeen years of operation, there has never been a serious accident at the Flying Circus. As Charlie Pearson says, "I'd rather be right than dead right." At 72, Charlie is the oldest pilot in the Flying Circus, and he flies the oldest plane, a 1929 Fleet Model 1. Or take another pilot, the Rev. John Frizzell, an Episcopal priest. The Flying Father, as he is sometimes referred to, says a special prayer for the pilots at the beginning and end of each season. Why would a priest find joy in being a pilot? Because he loves to fly. "A lot of people ask if I think about God up there," he says, "but you better believe I'm thinking about the plane!"

One practical reason for playing it safe is that the pilots are still paying off the mortgage on the airfield. With their liability insurance doubling in the past year, they can hardly afford to go crashing and burning all over the aerodrome. These magnificent men are just having a good time; they're not making any money here. They charge admission because, says John King, "we're going to fly our planes anyway, so we might as well pay off the mortgage."

But they'd also be the first to admit that they love performing for an audience. After the show, some fifteen planes are lined up in an impressive display in front of the audience. The heroes of the air stand casually by their machines, and pretty soon each one is surrounded by a small crowd. Tom Cruise in Top Gun couldn't have felt any prouder of himself than these swashbuckling pilots.

Still, it's not enough for some members of the audience to be near the pilots. They want to know what it's like to fly in an open cockpit biplane. And guess what? Before and after the show, anybody who wants to can buy a ticket to the skies.

I listened to one of the teenaged ground crew showing a young man how to use a parachute. She sounded as nonchalant as a stewardess pointing out exits: "Okay, should you find yourself out of the airplane, you'll want to stand on the wing, wait till the pilot says you're clear of the plane, and reach up and pull this, okay?" She packed him into the plane and sent him on his way. All that for nothing; he didn't even need the parachute.

I figured I'd give it a try. I donned a leather helmet and began to feel like the Red Baron, flying ace, until I put on goggles, which mushed my glasses into my face, and reminded me I was not. Even though I was told it was unnecessary, I gripped the bar in front of me as Jerry Reider and I bumped down the runway and took off in his Fleet 7. Since passengers fly in the front seat, I had a clear view ahead. I was Charles Lindbergh embarking on a new and daring solo flight. Then Jerry rolled the plane 90 degrees or so, and I though he'd suddenly forgetten all that stuff about safety first. With literally nothing but a piece of soft leather between my cranium and the ground, it occurred to me why people call it a once-in-a-lifetime experience. Never again, I vowed.

Later, on the ground, I heard pilots Reider and Frizzell talking plane talk while waiting to pick up more rides.

Reider: Why would a guy want to go up in a Stearman when he can go up in a Tiger Moth?

Frizzell (shaking his head): I don't know. The world's full of crazy people.

Woman (holding a ride ticket): I'm scared of heights.

Reider (laughing): Oh, so am I! THE FLYING CIRCUS

is 14 miles south of Warrenton on U.S. 17 (1 hour from the Beltway); P.O. Box 99, Bealeton, Va. 22712; (703) 439-8661. The show starts at 2:30 p.m. every Sunday, May through Oct. The aerodrome is open from 11 to 5. Admission to this weekend's air show and ballon festival is $8 adults, $3 children aged 6 to 12. Mass ballon ascension at 7 and again in late afternoon. Admission to the air show on other weekends: adults $6, children (under 12) $3. Rides last 10 minutes, and are given before and after the show: standard single $30, standard double $45, aerobatic $50, Piper Cub ride $17.50. Snack bar and picnic tables. Bring binoculars and sunglasses.