Detroit — Television ads portraying a 4-wheel-drive truck scrambling to the top of a hundred-foot-high pile of loose rocks defy both gravity and reality. Despite the macho image of such vehicles, the majority rarely find themselves in terrain any more treacherous than the average suburban parking lot.
No matter, the popularity of 4-wheel-drive cars and trucks, which waned during the heyday of the energy crisis, is returning, spurred by downsize, more fuel-efficient models.
American Motors Corporation, which will introduce a new, small version of its Cherokee and Wagoneer next fall, joins General Motors and Ford, which unveiled downsize 4-wheel-drive utility vehicles during the current model year.
Small pickups, including Ford's Ranger and GM's S-10 models, are also sporting the extra driving axle, new competition for the light, small 4 -wheel-drive pickup trucks from Japanese importers.
The suddenly renewed interest by automakers defies the sales trends in recent years. Last year sales of domestically built 4-wheel-drive vehicles were off some 40 percent from 1974, a time when the first impact of the energy crisis was being felt.
Fuel economy has been a serious drawback to the sale of 4-wheel-drive cars and trucks.
The extra transmission gearing, combined with the high-horsepower engines frequently specified by 4-wheel-drive aficionados, has kept them on the bottom rungs of the fuel-economy ladder.
Regardless, 4-wheel drive regularly takes from 15 to 20 percent of US light-truck sales, a market that automakers can't afford to ignore.
The revival has been paced mainly by downsize and imported models which trade off some interior room and off-road capabilities for small engines, diminutive size, and greatly enhanced fuel economy.
AMC, for example, projects fuel economy in the 25- to 30-mile-per-gallon range for its new Cherokee and Wagoneer sport wagons. Even with an optional 2.8 -liter V-6 engine (base engine is a 2.5-liter ''4''), the new Wagoneer is expected to give better than 20 m.p.g.
Already on the market is Ford Motor Company's downsize Bronco II, more than a foot shorter than the big Bronco, and powered by a 2.3-liter, 4-cylinder engine that's stingy on gas. Ford thus joins GM, which introduced the Chevrolet S-10 Blazer and GMC S-15 Jimmy last fall, both downsize versions of larger 4 -wheel-drive utility vehicles.
Adding to the imported pickup trucks already on the market, Mitsubishi intends to introduce a Jeeplike vehicle in the fall, the second Japanese auto company to do so, behind the Toyota Land Cruiser. Toyota also recently introduced a 4-wheel-drive version of the Tercel.
What's behind the resurgence in interest in these workhorse-inspired vehicles? Despite the apparent practicality of 4-wheel drive, which lends additional traction, theoretically useful in negotiating underveloped roads and driving cross country, 4-wheel drive in the hands of the average driver seems to give satisfaction more for the country-life, macho image it exudes than any particular need to get out of the mud.
Ford also points to the effect of the baby-boomers coming of age, and it's even counting on more women to join the off-roaders.
Dr. Marilyn King, Ford manager of contemporary markets, says: ''Many women today are discovering that a utility vehicle can match more aspects of their lives than can a car. They like them for carrying packages or sports equipment, driving in snow on suburban roads, or on off-road vacations. They find they fit a variety of family-weekend patterns.''
The increasing popularity of recreational vehicles, in fact, is spearheading the slow recovery of the domestic automobile industry after the worst recession in 50 years.
The overall RV market, which includes motor homes as well as the off-road cars and trucks, is up substantially this year, apparently ending a slump that hit during the first oil crisis.
But the rugged off-roaders have been joined more recently by a noticeable number of more-or-less conventional cars that also power all four wheels.
Unlike the Jeep-style utility vehicles, 4-wheel-drive passenger cars are rarely, if ever, seen off the road. Regardless, the additional traction is sometimes advantageous in snow, rain, or on marginal roads.
AMC developed two derivatives of its passenger cars with 4-wheel drive, the Eagle and Spirit. More recently, Volkswagen of America began importing the exotic Audi Quattro, perhaps the ultimate in 4-wheel drive. And around the first of the year it will introduce a 4-wheel-drive version of the Audi 4000, sometimes referred to as the ''baby Quattro.''
With a 156-hp. engine, the Quattro appears to need the all-fours technique just to keep the power on the ground. It is capable of some 130 m.p.h. and accelerates from 0 to 50 m.p.h. in 5.3 seconds.
At a suggested retail price of $35,000, the Quattro easily takes the prize as the most expensive, as well as the fastest, 4-wheel-drive vehicle on the road.