An estimated crowd of 5,400 people in 1,800 customized vans invade this tiny resort town on the Potomac for a weekend "Van Fest" - four days of sometimes drunken revelry billed as "the third annual Sun 'n Suds Boogie."

The vans, sporting customized paint jobs and airbrushed murals wall-to-ceiling shag carpeting, stereos, CBs, and bars stocked with Southern Comfort, began arriving Friday night in mile-long caravans from California, Michigan, Illinois and the East Coast.

The rules were simple. No drag racing, no fireworks, no nudity.

By early Sunday afternoon, every rule had been violated.

Barechested young men and women, most between the ages of 20 and 30, strolled through the dusty festival grounds at the Colonial Beach Dragway smoking marijuana, taking swigs from Tequila bottles or sitting under tents bathed in the blaring rock music that emanated from the nearby open vans.

Firecrackers went off periodically while the souped-up racing vans burned up the track in spontaneous drag races.

The end-of-the summer festival was open only to owners of these vans (estimated cost: $10,000) who paid $25 at the gate for a "once-in-a-lifetime weekend" featuring a Ms. Wet T-Shirt Contest, live rock-and-roll, Teeny Bikini contests and a Show 'n Shine custom van show.

On arrival, the various van clubs pulled their vehicles into circles, wagon-train style, and hoisted banners proclaiming their allegiance: there was the Kepone Truckin' Van Club from Hopewell, Va, the White Rose Jammers from York, Pa. and the Sky High Truckers from Norristown, Pa.

Concessioneers hawked everything from T-shirts to tattoos, along with straw cowboy hats, belt buckles, van accessories and drug paraphernalia. Scattered throughout the fairgrounds were 20 Port-o-Jons, two shower areas and 10 off-duty Virginia State prison guards there to provide security.

The concessioneers were almost superfluous though - the vanners brought most of the necessities of life along with them: food, wine, Frisbees, pets, babies and volleyball nets. They wore T-shirts ("If You Ain't Got A Van, You Ain't Worth S - ") and their vans sported bumper sticker slogans like, "If This Buggy's Rockin', Don't Bother Knockin'."

Joey Greer is a 22-year-old carpet layer from Warrenton, Va. He earns $10,000 a year and owns a $12,000 van.

"I gave up my Harley (motorcycle) for a van," he said.

"That's nothing," said his companion, "I gave up my wife for a van."

Greer is wearing a black leather vest, and faded jeans, silver bracelets, rings, and has shoulder-length hair. "A bike is like riding on a bird," he said. "But my van is my own personal party room."

Greer is a member of the Blue Ridge Runners, a Warrenton van club. "People come to van-ins to party," he said. "It's one of the few places you can go crazy. Nobody bothers you."

In fact, the town of Colonial Beach (whose winter population of 2,500 residents swells to 8,000 during the summer months) welcomed the vanners with open cash registers. City manager Joe Dune estimated that the four-day festival would pump $250,000 into the town's economy. The main industry in Colonial Beach, dubbed "Playground on the Potomac" during the '50s gambling boom, is now fishing and crabbing.

During three days of the four-day-bash, the local 7-Eleven store sold over 4,000 cases of beer. The Colonial Donut Shoppe sold out completely within an hour after they opened Saturday morning. Bags of ice that the distributor bought for 50 cents apiece were selling for $2 on the festival grounds.

Saturday's parade attracted the townspeople, mostly retirees, who waved to the yelping vanners from their cottage steps. "We love you," they called, waving handkerchiefs from lawn chairs.

Police Chief John Anderson said he had received only two or three complaints. "But you could bring the pope in here," he said, "and somebody wouldn't like it."

This Sun 'n Suds Boogie, along with two other East Coast van-a-thons named "Van Fest" and "Firecracker Boogie," are the registered trademarks of the Dean W. Moore Co.

But despite the popularity of these events, Moore, a 47-year-old auto show producer and exbeauty pageant judge from Harrisburg, Pa., is not well-liked by some members of the van community who complain that his shows are badly organized.

"They may not like me," Moore said, "but they follow me." Moore's Van Fest in Waynesboro, Va. drew more than 6,000 vans and 20,000 people over the Memorial Day weekend and was so rowdy he was forced to cancel his 4th of July Firecracker Boogie which was to be held in Raphine, Va.

The entrepreneur, who sports salt-and-pepper corkscrew curls and tight jeans, says his shows gross $500,000 a year.

Moore, a married man with two children and an eight-grade education, owns a home in Harrisburg, and a condominium in Mexico. He visits Las Vegas once a month and claims he keeps a sawed-off shotgun in his office. Last year he said he earned $100,000.

"I believe in vans. It started in California and came East a few years ago. People tell me these van fests are dying, but baby, they're just getting bigger," he said.

The promoter said he owns a customized van but would never think of bringing it to a truck-in. "I'm only in this for the money," he said. "I'm not here to have fun."

At 3 a.m. Saturday night, the camp-fires were still burning.

There were, however, two broken bones, one snake bite, assorted cuts from broken beer bottles, piles of trash, layers of litter and several thousand cases of too much sun and suds.

"By the end of this weekend you'll see a lot of bandages on people," said 23-year-old Carol Miller, whose husband Duke had set up a tattoo parlor in their customized van.

The Millers and their three children belong to a nomadic entourage of artistic gypsies known as Wanderin' Act. The 11 members live in the summer and carnivals in the winter.

"It's a hard way to make a living," Miller said. Posted on their van was a sign - "Babysitter Wanted. Must Travel."

Down the road, Teddy Bear from Hopewell, Va. still was showing off his 1935 customized Ford Sedan Delivery. Teddy Bear's real name is Ronnie Janosik, and he is typical of many of the festival-goers who do custom van work as a hobby.

"I've got a Mustang engine, hardwood oak floors, a Sanyo 1490 stereo system and all the Schlitz I can drink," he said, parking his 300-pound body behind the wheel. "I've also got a wallful of trophies back home."

Sunday afternoon, while some vanners sunned themselves at the pool-side of a local hotel, others at the dragway tried to explain what the weekend was all about.

"It's the gathering instinct," said one. "These people are here because they want to belong to something. A lot of them are ex-hippies, people from the '60s who don't want to grow up yet."