The theory is that stock car racing had its roots in the dark days of Prohibition, when good old boys back in the hills loaded up hot cars with moonshine for a high-speed race into town.

Today stock cars are featured on Wide World of Sports, purses are up in six figures and David Pearson and Richard Petty are folk heroes.

So much for the stocks as the people's sport.

Rapidly emerging as successor is the tractor pull, a high-powered romp in the dust that brings together urban grease monkeys and down-home farmboys.

Five years ago tractor pulling was something done out in the Midwest, the natural offspring of the centuries old horse pull. Folks in the East heard about it and some farmers here decided to give it a whirl.

Born of that effort was the Heart of Maryland Tractor Club, which Saturday ran its 17th competition of 1977, with more than [WORD ILLEGIBLE] and drivers from Maryland Pennsylavania, West Virginia and Virginia.

An more than 1,000 people shelled out $3 a piece to cheer them on from the rough-hewn wooden bleachers at the Charled County Fairgrounds in La Plata, Md.

It costs $10 to enter a tractor in any given class. The top prize to each winner at La Plata was $125, with lesser cash awards for the next four finishers.

That means Frank and Jim Stifler of Joppa, Md., put the $10,000 machine they built by hand on a trailer, dorve the 100 miles to La Plata and sheled out $20 to enter one race apiece. Maximum winnings; $250. Maximum loss: a pair of blown engines.

The tractor pull consists of dropping a sled loaded with iron weight across a dusty dirt track. He who drags it the farthest wins. If two or more drivers haul the load clear to the end there's a pull-off, where the load is increased.

Each attempt ends with ear-splitting engine strain and dust flying in the air as traction fails and machines grind to a halt.

The rig the Stiflers put together is about as far removed from a farm tractor as you can get at least until someone outdoes them. It looks more like the funny cars that spice up drag races.

Mounted on a pair or stock steel braces that make up the front end are twin polished, ported and chromed 454-cubic-inch Chevy V8s.

The Stiflers are the newer half of the tractor-pull crowd - the nonfarming faction. Jim Stifler is a salesman and Frank is an ironworker.

They compete in the "open" category. That means whatever wild concoction the motormad inventor can devise, within certain weight limits.

The "opens" are crowd-pleasers. With their tremendous power they send the huge rear wheels into spinning, dirt-throwing frenzies as they drag a 42,000-pound sled along the 300-foot course. Whether they make it to the finish line depends on the "bite" the big tires get. Loose dirt stops them cold.

The traditional farmere get their kicks in the stock class.

Jim Harbough, a young dairy farmer from Thurmont, Md., brought his creation. "The Eyesore" down for the day. It's a 1950s vintage John Deere diesel that was burned out in a barn fire. He rescued the salageable pieces and rebuilt it "as a toy."

"The Eyesore" is exactly what its name implies. Harbough never painted it after he got it back together, but Saturday he left in untended at the weighing station and some kindly fan came along with a can of spray paint and gave it some zebra stripes.

"If you see that guy, point him out to me." Harbaugh said with a laugh.

He could affort to laugh because he was still in first place weil into the 7,000-pound stock tractor races. Later he was caught and he ended up third in the class, none of which seemed to matter much.

Farmers work hard, you see, and when they take a day off it takes a lot to upset them.

The next stop on the tractor-pull circuit is Aug. 5 at the Hagerstown drag strip. The big tractor actors will be on hand again Aug. 24-25 for Montgomery County Fair in Gaithersburg. Bring along a picnic lunch and a wet rag to sponge off the flying grit. And earplugs, if you have them. CAPTION: Picture 1, Ivan Barnsley and his open classification tractor "Wildwood Weed" dig in while pulling a 42,000-pound loal at La Plata, Md. By Angus Phillips - The Washington Post; Picture 2, Eddie Horman of Frederick, Md., drives his $30,000-plus "Kay's Delight Turbo" through its paces. By Angus Phillips - The Washington Post