The ground-effects cars may start a ground-effects revolution in the Indianapolis 500 if Johnny Rutherford's shining yellow ground-effects racer wins the $1.3 million race that, come Sunday morning in front of 350,000 spectators, will send seven winners flying 200 miles per hour in their ground-effects cars.

Did someone mention ground effects?

Of the 33 starters, 15 will drive a model of the ground-effects machine that is the racer of the future. Anything that isn't a ground-effects car here Sunday might as well be a Greyhound. Rosie Ruiz will win this race by subway before anything besides a ground-effects car does.

Rutherford, Mario Andretti and Bobby Unser -- the three fastest qualifiers -- are in ground-effects cars. So are the other four former winners: A.J. Foyt, Al Unser, Rick Mears and Gordon Johncock. If we add the names of Danny Ongais, Johnny Parsons and Jerry Sneva, we have filled the list of possible winners Sunday -- and all are in ground-effects cars.

Did someone ask what is this ground-effects thing?

"It's very simple," said Jim Hall, the builder of Rutherford's car, the man who revolutionized all American racing a decade ago when he put a wing on the back of a race car.

"If you look under the car, you see there is a throat at the front that lets in air as the car moves over the track. Like this."

Here Hall pressed his palms togethr and then moved the fingers apart, creating the throat effect.

"Air comes under the car through this throat. As it moves under the car at very high speed, the air expands as it goes toward the back. The molecules grow apart. By the Bernouli principle, the faster the velocity of air, the lower the air pressure. So we're creating a vacuum, or trying to, under the car.

"That vacuum then sucks the car down to the track."

So effective is this creation of a vacuum that Hall once proposed a television commercial starring one of his Chaparral 2-J road racers.

"I wanted to drive the car on the ceiling," Hal said. "We could have made a helix track, one of those spiral things, and driven the car upside down on the ceiling. It would stick to the surface that well. It would have been a spectacular TV commercial, wouldn't it?"

The effect of the ground-effects prinicple is to give the Indianapolis cars superb cornering ability. The speed of racers always has been limited by the necessity to turn corners. When Johnnie Parsons won the 1950 Indy 500, his roadster's tires were 4 1/2 inches wide. His son Johnny will ride on rear tires 16 inches wide Sunday.

And now those wide ties have more help than ever. The vacuum under the car pulls the machine down. So it goes through the turns much faster. There is less slide. A car that can run on the ceiling certainly can run right side up on an 11-degree banking.

That is critical this year especially, for the United State Auto Club has changed its rules on the amount of "boost" cars can use in their turbo-chargers. Boost has been cut from 50 cubic inches to 48. Straightaway speeds are down slightly as a result; through the corners, though, the ground-effects cars are as fast as last year's conventional models.

The better handling in the turns is important not only for speed. It may be the difference between life and death. Some drivers are worried that the reduction in boost (most of these men ran at 60 cubic inches all last season, giving their cars 100 horsepower more than they'll have Sunday) will mean they have to run flat-out all day to keep up. If they run flat-out, they have no reserve of speed for use in emergency situations when they need to move away from trouble.

That's why it will be nice to know that a ground-effects car, glued to the racing surface by that vacuum, will react immediately to steering.

While the ground-effects car made its first appearance at Indianapolis last year -- Al Unser led for 85 laps in Hall's wonder until the transmission broke -- the principle was proven effective long before by Colin Chapman with Team Lotus in Formula One racing and by Hall himself

Hall, 44, is a lanky Texan who always seems to be squinting into a sunset. A mechanical engineer, he drove his own road racers for a decade before getting out of the cockpit and sitting down full time at the drafting board. You can find him in Johnny Rutherford's garage every day in May. He's the one in the straw cowboy hat. He's thinking.

Almost 20 years ago, he thought, "If you've got all these forces, why not make them work for you?"

He was thinking of aerodynamic forces.

All race car builders were confounded by aerodynamics. They didn't know what to do about the awesome pressures created by moving a bulky automobile through the air at speeds over 100 miles per hour. What they did, mostly, was try to deflect the air with assorted low-slung noses, long fins and slanted windshields.

"Mercedes, Porsche, Ferrari all fought what they considered to be a negative force," Hall said. "They concentrated on things to reduce that negative force. They lowered the bodies, extended the tails, rounded the edges."

Inspiration often visits without kno cking. "It just popped into my mind to take these 'negative' forces and make something positive out of them," Hall said.

Having driven around corners at speed, he knew he thanked heaven and Goodyear, maybe not in that order, for making his trip a safe one. Every racer wants traction, more traction.

"So I put a wing on a car, just to see what would happen," Hall said.

Voila! Eureka! Well, how-dee! By inserting a wing into that turbulent air over a race car, Hall created a force that pinned the rear end of the car to the track better. "Downloading, he called it. Pretty soon, every car on every track had some sort of wing at the back. Grandmothers drove to the grocery store in Plymouths that looked like Carl Yarborough hand-me-downs.

But Hall wasn't through thinking yet.

The problem with a wing is that while it helped stick the car to the track in the turns, it created wind-resistant drag that slowed the car down the straightaway.

So Hall made the wing movable. The driver, like an airplane pilot, controlled the wing. Down the straights, the driver moved the wing so it presented a thin edge to the air. In the corner, he set it so it caught the air.

Then, in 1970, Hall came with the Chaparral 2-J, a technological development so superior to its contemporaries that inside a year, it was made illegal. Hall had built two fans under the car to help create the ground-effects vacuum. Imagine your lawnmower with two blades turning. You got it.

"It was much faster than anything else on the Can-Am circuit," Hall said. "They ruled it off because it had a 'movable aerodynamic surface,' they said. That was bull. That rule had been written for my wings, not for my fans.All they had to do was say, 'We don't want to run this concept.

Could that happen at Indianapolis?

Could Hall's adaptation of Chapman's ground effects idea be so successful that a Rutherford runaway would cause USAC to outlaw such cars?

"They'll be regulated probably, but not outlawed," Hall said. "You don't outlaw an idea. Once an idea is conceived, it's part of the world, a living thing. It's just a matter of putting it to work in the best way you can."

Unless the unforseen happens -- at 200 mph. . .with 10 rookies in the field . . .with these fragile machines in terrifying combat, the unforseen can be catastrophic -- Johnny Rutherford in Jim Hall's beautiful car will win this Indianapolis 500.

They have done a masterful job of transforming an idea into reality. Rutherford, a two-time winner here and a driver of unquestioned skill, qualified a full mile per hour faster than anyone else -- a full mile per hour in a game in which speeds are so close together they are measured down to the last thousandth of a mile per hour.

"We're probably better set up for the race than anyone else," Hall said. "Roger Penske's outfit has three good ones -- Andretti, Bobby Unser and Mears. That's a good race team, but we've got an edge on them."

You might ask what the edge is.

You might ask, but Jim Hall won't say.

"Roger Penske could look at our car and he couldn't tell exactly what we're doing different from him," Hall said with a sly smile. "It's got to do with sizes and shapes and location. Y'know, if you think you got something the others don't, you don't go telling them, do you?"