There's nothing like a country jamboree to bring out the shrillest hog call, the speediest corn-husking or the most prodigious projection of an expectorated watermelon seed.

And when you get 15,000 people together and toss in lots of country music -- and autograph opportunities -- what you've got is a thick slice of Americana.

A Pepsi commercial couldn't have produced more smiling faces in one place than the Bull Run Country Jamboree did yesterday at Bull Run Regional Park, near Centreville. It was the second year running that the Northern Virginia Regional Park Authority has thrown the bash, and attendance was up by several thousand over the 1980 figure.

From center stage you were looking at the image of country -- a swarm of glistening bodies hemmed in by kids and coolers, laden with cameras, submitting to the hot sun. For today, they were living out Barbara Mandrell's slogan about being "country when country wasn't cool."

The jamboree was like a bluegrass festival with an electric beat, a chance for family and friends and lovers to cook together and catch five middle-of-the-line country acts that have had No. 1 singles in the last year, including T.G. Sheppard, Razzy Bailey, Ronnie McDowell and Charly McClain.

This being a family affair, it helped that David Frizell and Shelley West kicked off the afternoon's music; West's mother is country superstar Dottie West and David's late brother is the country legend, Lefty Frizell. In country, the circle is often unbroken.

The best spot, the one that true fans were loath to give up, was the chest-high fence around the backstage area. That's where the magic was, since backstage is usually a place well behind closed doors. But the stars of this show mingled freely with radio KIX-Country jocks, jamboree volunteers and sponsors, and all manner of police who had little to do but look at the stars themselves. A reporter was asked for his autograph on the off-chance that he might be somebody.

After their set, Frizell and West spent more than an hour away from the protection and shade of the stage awning signing autographs. People brought all kinds of things for the stars to sign -- shirts, hats, empty Coke cups, casts on broken arms and legs, glossy photos being sold for $1, posters that were often bigger than the young fans carrying them. With an arsenal of inexpensive and expensive cameras, they crowded for photo angles like White House press corps veterans.

Face-to-face with the musicians, the fans were polite and a bit awestruck. Some stammered questions, while others spoke with a neighborly familiarity. On the fan side of the fence:

"How 'bout a big smile, Shelley?"

"David, come over HERE."

"Thank you, thank you, thank you."

"God bless you and keep on singing."

"Can you sign it 'to Pat'? She's sick and can't make it today."

"I love your momma!"

"That's a nice compliment," Shelley West answered the last remark. To a shy teen-ager who whispered in her ear, she said, "Okay, give me a gift," at which point the boy pecked her on the cheek and disappeared into the crowd.

It was an enthusiastic crowd that milled about the food and souvenir stands, a crowd that consumed more than 1,400 pounds of beef and pork, more than 300 pounds of french fries, more than 3,500 hot dogs and hamburgers, and God-knows-how-many gallons of soda pop.

And it was a well-behaved crowd for the most part, too, despite the hoots and rebel yells and Confederate flag-waving.

"We're just a friendly bunch of country boys," said Patch Holton of Nottoway County, Va., Holton, wearing a studded leather vest and cutoffs.

There were plenty of tattoos and "I love country music" buttons everywhere. One fellow, David Cogswell of Arlington, had one pinned to his bare right nipple.

"Man, that hurts!" he told friends after a few seconds. "But I really love country music -- especially Merle Haggard and Hank Williams."

Perhaps one of the reasons everything went so smoothly at Bull Run was that there was so much to do.

In back of the stage, various roped-off areas featured old-time country competitions.

There was corn-husking (the winner husked 20 ears in two minutes -- a thumb-blistering pace) and hog-calling (a most unresponsive hog -- who knows how they determined the winner?).

There was a greased pole with a sawbuck taped up top. All morning, teams of family and friends slithered part way up the poll, slick with axle grease, only to slide sloppily down again. But in the afternoon, when the bottom half of the pole was a little less slick from all the fruitless efforts, a savvy team from Manassas -- the same team, in fact, that took the prize last year -- scooted to the top and nabbed the $10 bill before oozing down to loud applause.

And there was a fellow who spit a watermelon seed 35 feet. Period.

But perhaps the most consistent attraction of the day -- besides the music, that is -- was the mechanical bull.

The crowd's favorite seemed to be a giant of a man named Larry Roadcap, from Page County, Va. Roadcap's first stint on the bull was spectacular only for the arc his 6-foot-5-inch frame made when he was thrown.

But his second bid was more successful, and he stayed up for the whole ride.

"I don't care about prizes," he said, flexing his left bicep. "I just have this satisfaction now. And I'm gonna get more satisfaction yet from this music."