Call it the rule of four. Since the late 1880s, when the four-wheel motorcar created by Gottlieb Daimler turned out to be a more stable platform than the three-wheel version developed almost simultaneously by rival Karl Benz, automobile design has favored four of everything. Three-wheel cars have been given serious attention by men like Buckminster Fuller, Englishman H.F.S. Morgan and even German aircraft designer Willy Messerschmitt, but none has ever been a popular success. Four is the ideal number of wheels for road-borne vehicles, and there is no reason to believe such a set-up will be displaced.

The rule of four doesn't stop at the number of wheels on a car. Four doors, for example, are also a staple in the world of cars. Statistics are incomplete on the subject, but it is worth a wager that since automobiles began to be seriously produced around the turn of the century, a majority of those built have had four doors. And so it goes: four wheels, four doors, four-speed transmissions (remember the 1960s fascination with the phrase "four-on- the-floor"?), four cylinders, even the "four-holer" Buick Roadmasters. The number has been a presence in the world of cars since the beginning, and now, as we edge toward a new century, it promises to become even more important. For example, the four-speed automatic transmission is about to completely displace the old three-speed automatic transmissions such as Hydramatics and Torqueflites that were basic to the industry for two decades. With the advent of microprocessors, engines can be matched with four-speed automatics to offer maximum economy and performance, from highway travel to urban stop-and-go.

Each day, four-wheel drive becomes a greater factor in the automotive product mix. Any number of carmakers, here and abroad, are following the lead of manufacturers such as Audi by offering four-wheel drive in passenger cars. The vast majority of passenger cars are pushed by the rear two wheels (rear- wheel drive) or pulled by the front two wheels (front-wheel drive). Four-wheel drive, in which all four wheels drive the car, was heretofore believed to be useful only for off-road addicts, campers, hunters and construction workers. Then exotic machines like the Audi Quattro opened a new market for drivers who desire maximum road-holding under all weather conditions. Adapting four-wheel drive to passenger cars has brought a revolution in ease of operating. Instead of stopping the car, getting out and locking in the front hubs by hand to activate four-wheel drive, the new systems can be controlled from the driver's seat by flipping a switch -- two-wheel drive for normal conditions, four-wheel drive when the going gets tough. Numerous carmakers, including Ford, Porsche, Toyota, Mazda and Subaru, are making four-wheel-drive passenger cars, and more manufacturers are sure to follow, including Mercedes-Benz, which is working on a computer-controlled system that will automatically select the proper two- or four-wheel drive depending on the weather and road surface. The four- wheel-drive technology owned by AMC/Renault's Jeep Division was a primary reason for the purchase of the firm by Chrysler Corp. Lee Iacocca, like dozens of his counterparts in the worldwide car business, believes four-wheel drive will become a major market factor in years to come.

Honda recently introduced four-wheel steering on its Prelude. The Japanese have been fascinated with this set-up for a number of years, so look for it to be offered soon by Toyota, Nissan, Mazda and others. American and European manufacturers are less enthusiastic. Four-wheel steering permits the rear wheels to turn in conjunction with the front pair, enhancing the maneuverability of the automobile, especially in tight urban situations. Honda also touts the system as an adjunct to handling on the open road, but, frankly, I can see little benefit in this application. The extra weight and complexity of the linkage to turn the rear wheels a few degrees while cornering is simply not worth the enhanced steering. Jockeying in a parking lot is another matter. Four-wheel steering can make the squeeze into a shoebox-size parking space much easier. Nevertheless, four-wheel steering edges close to being a technological gadget, more useful in cocktail-party conversation than in real-world motoring.

Not so with the recently introduced four-valve engines that are now appearing on many makes of automobiles. General Motors, for example, is planning to make a big deal of the new Oldsmobile Quad-Four, a four-cylinder engine embodying the system. It is simple enough. Most conventional internal- combustion power plants use two valves per cylinder -- one to ingest the air-fuel mixture, the other to exhaust the gasses after the fuel is burned. For years, exotic racing engines have been utilizing four valves per cylinder -- two intake, two exhaust. The logic is elemental: The more fuel that can be burned, the more power that can be generated. While the technology has long been understood, it took the electronically controlled ignition and fuel-injection systems of today to make four-valve engines practical for everyday applications. Prior to the involvement of microprocessors, four- valve engines were simply too ravenous in their appetite for fuel, which in turn produced unacceptable levels of noxious exhaust. Now computers can meter the fuel with such precision and burn it with such efficiency that exhaust emissions are minimized.

You see, then, how the rule of four rolls on? Now there are four-wheel disc brakes, four-wheel independent suspensions, four-wheel anti-skid braking systems and four-speaker stereos. As somebody said, the more things change, the more they stay the same. ::