The noise batters the ears and the blurred flashes of color under the arc lights force the eyes to focus and refocus on the yowling, roaring, sliding berserk machines blasting by at 130 miles an hour. Across the narrow dirt track, 20,000 fans are on their feet, screaming and waving as a burly young man named Steve Kinser slashes by slower cars on his way to victory.

This little bubble of light and sound is in the middle of darkened cornfields in a place called the Marion County Fairgrounds, near Knoxville, Iowa. People here call it "the world's center of sprint-car racing." It is a bowl of dirt, one-half mile in length, its origin dating back to the 19th century when the hooves of trotters and thoroughbreds hammered on the track's loamy surface. Now horseshoes have been replaced by horsepower and the spectacle is a rare one indeed. This is a country game at the ragged edge of automobile racing, using crude "sprint" cars and played with very few rules.

Folks have come from miles around, from Des Moines and Cedar Rapids and Sioux City and Waterloo, to witness the spectacle of speed and power and controlled violence at this little half-mile track. Sprint cars are some of the most dangerous, challenging machines known to man. Barely more than spidery tubular chassis and rudimentary bodywork, mounted on giant tires (two feet wide in the rear) and topped by a wing the size of a barn door, the classic Outlaw sprinter is a bucking bronco on wheels -- 1,300 pounds of metal propelled by a 410-cubic-inch, alcohol-burning, Chevy-based, all-aluminum V-8 engine generating more than 700 horsepower.

Unlike the ultramodern Indianapolis and Formula 1 cars, which carry their engines mounted behind the driver, sprint car engines are in the traditional up-front position. Unlike the aerodynamically sleek stock cars of NASCAR racing or the curvy sports cars of IMSA racing, sprint cars are not pretty -- most are a collection of odd angles and flat metal surfaces.

The drivers of these cars are unknown in the cities, where the masses rarely get to see their skills on TV. But in small towns from Pennsylvania to Iowa, a driver like Steve Kinser is as well known as a Moses Malone or a Jay Schroeder is in Washington.

Kinser is a 29-year-old former state wrestling champ from Bloomington, Ind. His race car is owned and maintained by his uncle Karl. Together they have won more races than any team in the business -- hundreds and hundreds of five- and 10-lap qualifying "heats" and 20-lap "features." Running as many as 90 different tracks in a season, from coast to coast, Kinser has been able to earn more than $300,000 a year, which has been enough to inspire thousands of youngsters to follow in his footsteps.

No one really knows how many small, local oval tracks dot the nation. A publication called the National Speedway Directory lists nearly 2,000 quarter-, third- and half-mile tracks, but it's generally believed there are more than that. Each track runs weekly programs of jalopy, stock, modified, sprint and midget racing in which untold multitudes compete.

A conservative estimate would be that each track has 200 drivers who regularly appear -- 40,000 nascent Steve Kinsers or A.J. Foyts spinning round and round in this expensive and dangerous enterprise. And fans? The spectator turnout is a mystery, though the major forms of car racing -- Indianapolis- type competition, stock cars, drag racing and sports-car racing -- generated attendance of 8.3 million last year, and the 1987 season is expected to exceed that.

The World of Outlaws sprint-car series (so named because in the 1950s anyone racing outside the sanction of the American Automobile Association was labeled an Outlaw), which is the major league of this type of competition, ran 815,000 fans through the turnstiles last year. Uncounted thousands of fans show up over the 40-weekend racing season at hundreds of other tracks, where attendance figures are not necessarily kept. Suffice it to say there are millions of fans who compose an invisible segment of the American sports mania.

Despite the numbers, the scene remains rural. For every race track located even in a medium-size city such as Charlotte, N.C., or Daytona Beach, Fla., there are a hundred in burgs like Williams Grove, Pa., Oswego, N.Y., and Martinsville, Va. The soul of the sport is centered in rural America, where the automobile is loved and understood, where driving takes place away from clogged freeways and alarm systems that protect stereos.

There was a time not long ago when the county fairgrounds of America were the minor leagues of automobile racing. Kids climbed aboard sprint cars 30 years ago dreaming of the grand day when they would roll into the victory lane at the Indianapolis 500. Until the middle 1960s, when road racing specialists began to dominate the starting field of the 500, the traditional Indy car driver could trace his origins to a dirt track like the one in Knoxville.

It was a tough education. Sprinters took a terrible toll in lives until roll bars and giant wings were fitted in the mid-1970s (the wings keep the sprinters glued to the earth in the turns). The brutal flips that were common on dirt tracks would crunch drivers riding unprotected in open cockpits. Racing stars like A.J. Foyt, Mario Andretti, Johnny Rutherford and the Unser brothers, Al and Bobby, were as remarkable for surviving their apprenticeships in the lethal sprinters as they were for their driving skills. Looking at the 33-man starting fields of the Indianapolis 500 from 20 to 30 years ago reveals that one-third of the drivers ultimately died in dirt-track racing accidents.

Today, despite the protection of fireproof clothing, fuel tanks that won't burst on impact, special helmets and rollover gear, the danger has been diminished only slightly. Contemporary sprint cars are 20 to 30 percent faster than those of a couple decades ago. Impact speeds in crashes have increased.

It remains a compelling sight to see these monster cars rip around a half-mile dirt track. For four steamy nights of racing on the perfectly manicured speedway in Knoxville last month, the best sprint-car drivers tried to outdo one another for more than $200,000 in prize money. Steve Kinser and drivers such as Sammy and Jeff Swindell from Tennessee, Pennsylvanian Brad Doty, Californian Jimmy Sills and others navigated the tight oval flat out -- never lifting their accelerator pedals as they flung their flame-belching monsters around the low-banked corners in terrifying broadsides. Sammy Swindell was nursing a separated shoulder from a mishap in which his steering failed on a Tennessee dirt track and he slammed the wall, head-on, at 100 miles per hour. Any number of his fellow competitors were suffering a variety of aches and pains -- including the dreaded "red-eye," a unique hemorrhaging of the eyes caused by the g-forces involved in a sprint-car flip.

Those nights were full of unrelenting competition with no quarter asked or given, the timid and unskilled left behind in a barrage of flying dirt. At the front of the pack, the Kinsers and the Swindells pitched their bellowing beauties through the looping turns, sawing wildly on the steering wheels as they charged through the grit. And the crowd loved it.

People in rural America are a straightforward lot and they like their sport direct and to the point. Bravery counts. Simple values still count: the flag, apple pies and roaring sprinters.

As they say, "Run with the big dogs or stay on the porch." The folks in places like Knoxville understand things like that. ::