THE MOST heavily attended nonbetting sport in the United States is -- what? Baseball? Football? The answer is auto racing; and of the various forms of auto racing, Grand National stock-car racing is the single, most heavily attended series of races in the world. In 1980, more than 1.5 million spectators bought tickets to them, more than attended Grand Prix races worldwide.

Stock-car fans are drawn by the color, excitement and opportunity for vicarious participation offered by 200-mph races between drivers like Richard Petty and David Pearson, in cars that closely resemble the spectators' own. Kim Chapin's book documents the 30-year growth of Grand National racing from its earthy origins to a sophisticated, multimillion-dollar sport.

In one way, it's too bad that Chapin focuses so much on the early days, when stock car racing was redneck, rowdy and disreputable: some readers may not fully appreciate the virtues of the pioneers. Lance Reventlow, Barbara Hutton's driver-son, said after an encounter with one legendary hero, "Curtis Turner is a ruffian. And, I might add, a common ruffian."

The fact is, the roots of stock-car racing lie in the red clay around Dahlonega in Wilkes County, Georgia, where white lightning runners used to tear down out of the hills toward Atlanta with a full load of fruit jars. In the 1940s, the bootleggers depended on cars capable of outrunning the revenue agents, and on drivers who delighted in the sport of it. It was inevitable that they'd start to pit their ingeniously modified liquor-transporters against each other, gathering in cow pastures to race, drink and argue over who was the fastest of all. Chapin has talked at length with Tim Flock who, along with his brothers Bob and Fonty and sister Ethyl, was active in this period of transition from bootlegging to professional racing. Flock's scrapbooks and reminiscences offer a sensational view of the old days. On outrunning the sheriffs:

"When they got a deal that was known as a cowcatcher. Worked just like an ice tong. They could run up behind you on a hill and they'd bump you and it'd close on you. Then they'd put on the brakes; just keep ridin' the brakes. It'd stop you. . . So to stop this, we put the bumper on with two coathanger wires. They'd run up behind us and they'd put on the brakes and they'd pull the bumper, and every time it'd fall right off in front of their front wheels. By the time they got that damned thing untangled, the bootleg car's going on in to Atlanta . . . "

This story sounds wild enough to be apocryphal, and perhaps it is; but based on what I've seen of present-day stock-car mechanics' creativity, it could very well be true.

In 1950, the first southern superspeedway at Darlington, South Carolina, opened and a new era began. The National Association for Stock Car Auto Racing, Bill France's highly effective dictatorship over drivers and mechanics, put on the first Grand National race in 1949; in 1959, racing at Daytona Beach shifted from the famous strand to France's new 2 1/2-mile high-banked oval.

As top-speeds rocketed upwards, raw talent and recklessness were no longer enough to carry a driver to victory. And when the Detroit factories stepped into the the game in the middle '50s, the nature of the sport was permanently changed. Slowly, the drivers became professionals. The Detroiters, accustomed to big-business hardball, generated pressures which had nothing to do with how the game was played -- only with wins and losses

Chapin's research has been thorough. His interviews trace the genealogy of the sport from Flock to Fireball Roberts, who was as successful on the superspeedways as he had been on the dirt tracks; to Cale Yarborough, whose career was made by the Ford factory; to Dale Earnhardt, the 1980 Grand National champion, a second-generation driver whose sights were always set on success at the top. By Earnhardt's time, there was indeed a success to aim for. Today's top drivers are often millionaires and fly their own executive aircraft to the races. They are no longer regional heros, but national stars.

Chapin has incorporated a yeasty mixture of strong and outrageous characters into a book that even knowledgable racing fans will find revealing and informative. It may be a definitive history of stock-car racing, but as a work of literature there are rough spots. In attempting to penetrate the mysteries of a risky sport, Chapin lapses into the maudlin and melodramatic -- something the drivers themselves avoid. One sympathizes with the drivers as they struggle with unanswerable questions posed in an analytical, cool, objective language that is foreign to them. The fluent Bobby Allison is a prominent exception: "At the end of any race you have all but won . . . you begin to almost pray, 'Don't let anything happen to this car.' Or, 'I hope we don't have a caution where everbody else catches up.' It's an inner fear, a mental strain. It's like you're hearing strange noises and everything. You don't really hear the noises, but you're keyed up to the point that you can almost hear something trying to go wrong."

Southern language is notoriously difficult to transcribe with its dignity and flow intact, as well as its color, pronunciation and grammatical peculiarities. In this area, Chapin is no Eudora Welty. An additional complication is posed by terms and usages peculiar to the sport. "Getting a hold" or "a bite" and "going through a hole" have quite specific meanings that could stand explanation; in a few passages, drivers' descriptions of racing action have been somewhat misunderstood.

At the beginning of the book and occasionally thereafter, the writer intrudes too much. We really don't want to know that at the time news of Tiny Lund's death came on the radio, Chapin had "retired briefly to the bathroom. Then my friend pleaded through the door, 'Tiny Lund's been killed.'" Or, "A small part of me was secretly pleased that Tiny Lund had been killed on my time. . . . if Tiny was doomed by whatever capricious forces are at work out there, well then, maybe the tragedy of his death would help give focus to my current project." This reaction may be all too human but it is shocking, and if introduced, needs explication and interpretation.

The reader who perseveres, however, will find that his work is eventually rewarded with a pretty good understanding of what may be the quintessential American sport.