IF YOU hear names like Petty and Earnhardt at a race sponsored by the U.S. Lawn Mower Racing Association, it's pure coincidence. If the fans outnumber the flies at one of its events, it's considered a big turnout. Forget instant replay; if you miss it, you missed it.

And if there's ever a movie about an event sponsored by the USLMRA, don't look for Tom Cruise's name on the credits. Jerry Seinfeld, maybe. Or Jim Carrey.

The dirt track lined with bales of hay for safety at the Catskill Events Center on this blistering Saturday will remind few of stock car racing shrines such as Darlington or Road Atlanta and superstar drivers like the Pettys and Dale Earnhardt, though the tenth-of- a-mile, kidney-shaped race course is no more primitive than the strips where NASCAR racing was born.

In any case, don't try to tell people like 39-year-old Al Bitterman that their sport of choice is a little nutty or second banana to auto racing. Not when he has devoted hundreds of hours to preparing his racing mower and driven all night, 850 miles, from his home in Zurich, Ill., just to compete here in the Hudson Valley. "It started out just to be a fun thing, about four years ago," he says, standing in his trailer / rolling tool shop, whose walls are plastered with his press clippings and snapshots.

"My neighbor was going to junk this tractor," he says of the bright green, showroom-clean Gibson / Montgomery mower he races. He modified the 11-hp machine and zipped around the neighborhood with it. Then he heard about organized mower racing. The engine was soon replaced by an 18-hp engine, which was then modified to produce, he says, about 35 hp.

"Once I got involved, I got hooked, and now they can't get me off it," he says.

If you can tear the driver / owner / pit mechanics from their last-minute repairs and tweaks, however, they're happy to tell you about their machines; just prepare to be quickly in over your technical head in headers, carburetors, centrifugal clutches, stainless-steel valves and compression and pulley ratios.

They might look a little silly out there, those grown men (and an occasional woman) with their colorful helmets and all manner of racing garb, bouncing violently on little machines with no suspensions to speak of, their mufflerless engines popping and snarling, their rear tires sliding through turns and their front tires going briefly airborne as they accelerate. But the start of the first race brings the crowd of 200 or so ringing the track on overlooking hills to its feet.

Today there is only one (inactive) member of the association from Long Island or Queens and only one racer - a man from Astoria who just happens to be here with his wife, a freelance writer researching an article on mower racing. The racer is asked to ride a borrowed machine in an event short on contestants.

Otherwise, downstaters apparently are far behind the mower-racing curve.

But among the spectators are Bob Cosgrove and his wife, Jyl, from Copiague, who have a summer home in this region about 125 miles from the Whitestone Bridge.

They read an announcement of today's event in a local paper. "I said, 'We've got to see this.' " said Bob Cosgrove. Added Jyl, "Whoever thought John Deere would be a racing name?" It's serious stuff to mower racers, who bring their machines to events on trailers, in vans or in the beds of pickup trucks and, in some cases, set up tents and put down sheets of plywood to make "pit" areas. But if those Snappers and Toros and MTDs out there raising dust clouds on the track are basically the same as the machines that chug along at walking speeds on weekends trimming suburban lawns, some have been modified to go as fast as 65 mph. None will come close to that today, however, on this tiny track.

Daryll Bratton, who is 49 and drove here alone from Indianapolis to race "409," estimates he has spent 600 hours modifying what left the Ariens factory as an 8-hp tractor. He added a 13-hp Honda engine that probably is crowding 30 hp now. "I don't know what the top speed is," he says "but I have it geared for 50 mph." Like many involved in the sport, Bratton owns a mower repair shop. Which brings up the serious side of organized lawn mower racing; it has its roots in pure capitalism - product promotion. This event, like many lawn mower races, had in its title the name "STA-BIL," which also appears on banners around the track, on T-shirts and on racing mowers. STA-BIL is a gasoline additive for lawn mowers and other small machines, one of about 100 automotive chemical products of the Gold Eagle Co. of Chicago.

Gold Eagle and its public relations agency, Merton G. Silbar, set up the national mower racing association in 1992, says David Silbar, who works for the agency and is the son of its founder. It's modeled after a group in Great Britain, where, the association says, the sport was invented about 30 years ago - by three men over drinks in a pub, which you probably could have guessed. The association's president, Bruce Kaufman, works for the agency.

Other corporate sponsors have included the makers of Snapper lawn mowers and Citgo lubricants, Kaufman says. Local mower shops and other businesses sponsor some drivers. The California company Prolong Super Lubricants is fielding a professional team this year, and one of the four drivers, Bobby Cleveland, has come up from Georgia today to race one of six Snappers. (He will come in second, after Bitterman, in the day's first race, marked by a mishap when a machine loses a wheel and rolls over. The driver appears unhurt, and the mower is pushed off the track.) The association claims there has never been an injury worse than a broken wrist at its events, even though drivers have been known to "trade paint" in the heat of a race. An ambulance corps stands by. Racing machines are inspected before the events begin. "You've got to have really good brakes on these things," says 28-year-old Brian Burdette of Aberdeen, Md., here with his brother to race two machines. "For some reason," he adds jokingly, " they want you to be able to stop." All mowers must have operating "deadman" automatic engine-kill switches in case the rider falls off.

Drivers must wear helmets, eye protection, long-sleeved shirts or jackets, long trousers, gloves and over-the-ankle boots - outfits not quite suited to this oppressively hot and humid day. "I did six or seven laps out there [for practice]," said 45-year-old Dave Smith of Hazlet, N.J., who also owns a mower repair shop and will be racing a 12-hp Toro today. "The water was just pouring off me." The group claims about 1,000 members in five countries and is running events this year in 10 states. Two more major races are scheduled in New York: July 15 in Lowell (near Rome) and Aug. 26 back in Catskill.

The biggest prize at any of the association's races is a trophy; there are no cash purses. While the association is nonprofit, there are admission and entry fees ($5 and $10 per driver, respectively, today), and the money realized after expenses goes to charities or other worthy causes - in this case, the Kiskatom volunteer fire department.

Mostly, though, lawn mower racing is an amateur sport, and racers say they come for the camaraderie as much as the challenge. "If I didn't like the people I was racing with," said Bitterman, "I sure as hell wouldn't drive 800 miles to be here." As today's racing is about to begin, the town supervisor of Catskill reads a proclamation welcoming everyone. Then the "Star Spangled Banner" is played, and drivers line up a few feet from their machines for a "LeMans start," in which they sprint to their machines when the flag drops, start them up and start racing.

You might call it a grass-roots type of sport. Which brings up the subject of awful puns. Get used to them if you decide to participate in mower racing. Some racing events are called "mow downs" or "mowllennium mowdowns." Kaufman calls himself "Mr. Mow It All," racing machines have names like "Sodzilla," "Turfinator" and "Lawn Ranger," and the public is invited to events with the phrase "the mow the merrier." There are rules intended to keep the competition fair, as well as safe.

Machines are raced in classes by horsepower and other factors. Regardless of class, the engine's block - its core structure - has to be from a lawn mower or lawn tractor. That's to prevent someone from bolting a V-8 from a Chevy pickup onto a Snapper chassis and trying to race it as a lawn mower.

Attendance at races ranges from a few hundred to about 2,000, says Silbar.

Riders have to be at least 16 years old.

Not all events are as primitive as that in Catskill, where every seat is a bleacher and race officials stand on the back of an open farm trailer. National competitions (as opposed to regional competitions like this one) have been held indoors for the past few years.

And, while a quarter-mile or less kidney-shaped course is the norm, mower racers have done exhibitions at the Charlotte, Atlanta and Texas Motor Speedways - on pavement, for goodness sake. As few as two and as many as 20 racers are on the track at any one time. Today, 20 drivers have entered, with 25 machines.

While lawn mower races are not (yet) covered regularly by network TV, mower racing has made a cameo appearance on the TV series "Home Improvement." The cable racing channel Speedvision is scheduled to broadcast another series of programs on mower racing this fall.

If you're impatient, there is some brief race footage available on the association's Web site, www.letsmow.com, some of which was taken by a mower-mounted video camera.

On Saturday and Sunday, the sport will have its first international competition, in Lisle, Ill., near Chicago, when racers from the British association fly here to compete against this country's top drivers and mowers.

Few, if any, of the machines at that event or any other, however, will ever do anything as mundane as cutting grass. For one thing, their blades have been removed. Anyway, to mower racers, it would be akin to having a Thoroughbred racehorse pull a trailer full of peach pickers.