Audi reaches for a fresh image with its snappy 4000-S Quattro

Dropping down into the right-hand seat of a rally-competitive Audi Quattro, I pull the helmet over my ears and strap it. Reaching for the safety belt, I fold it over both shoulders and across my lap while rally champion John Buffam gives a hand.

Buffam is ready, the car is ready, and (I think) I am ready.

Buffam throws the car into gear, and we head onto the Vermont blacktop at the Sugarbush ski area some 40 miles south of Burlington and Lake Champlain. Buffam whooshes ahead of a slow-moving truck, and the ride suddenly becomes very interesting indeed as we head up a gravel-surface mountain road.

The idea behind the brief ride is to give a few automotive writers a touch of rallying a la John Buffam. The cup-winning Buffam throws the car from one gear to another as we surge uphill, swerving around bends in the road, the roar of the engine drowning out any effort at conversation.

In full control, the rallier (and his passenger) return to the starting point , satisfied that the car did its job. The car was a beefed-up 4-wheel-drive Quattro, introduced to the United States some 20 months ago.

Now Audi has installed the same all-wheel-drive system on the 4000, a smaller version of Audi's ''big machine.'' The 4000-S Quattro, which went on sale earlier this year in Europe, is the second stage in the West German automaker's move to all-wheel drive across its entire lineup. By 1986, it will drop the all-wheel-drive system into the all-new 5000, completing the job.

Why 4-wheel drive - or, as Audi engineers prefer to label it, all-wheel drive?

''The fundamental purpose of a motorcar is mobility in all weather conditions , regardless of the load being carried,'' says Joerg Bensinger, manager of chassis development for Audi NSU Auto Union AG. ''Irrespective of load, the traction developed by a car with 4-wheel drive is about twice as great as with a car having only two driven wheels.''

What he's saying is that 4-wheel drive makes it safer to drive on snowy or gravel roads. That's the point Buffam was making on that fast-paced climb up the mountain. There was no snow or ice around, but there was plenty of banana-peel-like gravel.

The car was disciplined at all times. There were no surprises in how it performed.

Four-wheel drive allows a higher cornering speed as well. ''It distributes the tractive and engine-braking forces between four wheels and so places far-lesser demands on the adhesion of the tires,'' Bensinger says.

With the Audi all-wheel-drive system, there is no penalty in fuel economy, its engineers assert, and at higher speeds, the cars are said to get even better mileage than a 2-wheel-drive car, either front or rear-drive.

As with the all-wheel-drive Quattro coupe, the 4000-S Quattro employs a third differential - the only carmaker to use such a system in its drive train. Unlike other 4-wheel-drive vehicles, the Audi 4000 is as low to the ground as any standard-drive automobile, yet the car is always in 4-wheel drive. Ground clearance is a sparse 51/2 inches.

''You don't have to buy a stepladder to get into it,'' smiles Peter Fisher, head of the Porsche-Audi division of Volkswagen of America Inc.

The Audi system also employs a lock on the center and rear differentials which can be used under extreme road conditions - deep snow, for example - for better control. Under normal road conditions, the lock should never be used.

The second-generation, 5-cylinder, 2.2-liter engine in the fuel-injected 4000 -S produces 15 percent more power than the engine it replaces and zips from 0 to 60 m.p.h. in 9.5 seconds. Top speed is 115 m.p.h., compared to 130 in the Quattro coupe. A turbocharger, such as in the big Quattro, would give a lot more punch, but that's still down the road.

''I like to drive my Quattro,'' admits Mr. Fisher, ''but most people don't need that much boost.''

Even the new Audi 5000-S, introduced earlier this year, won't get a turbo till the first of the year - about the time the 5000 wagon arrives in the US.

The present Audi 4000 has been on the road for a half-dozen years. In 1985, it will get new sheet metal, but nothing big. A turbo will probably arrive with the all-new 4000, which is not due till the 1986-model year. The '86 Audi 4000 will have more resemblance to the 5000, but with an even lower coefficient of drag. At 0.42, this coefficient in the current 4000 is very high when compared to 0.33 in the new 5000.

There will not be an automatic transmission in the Quattro coupe or the 4000 -S Quattro until 1986.

The all-wheel-drive Audi 4000-S is sticker-priced at $16,500, but it includes everything but a two-way power sunroof and metallic paint.

The Environmental Protection Agency figures the mileage in the 4000 at 21 miles a gallon in the city and 28 on the highway. In a drive home from northern Vermont, I got in the low 20s, but this can be expected to go up as the brand-new engine loosens up.

Audi management expects to sell some 3,000 small Quattros in the US next year as it reaches hard for a new image, badly hurt by serious problems with some of its earlier cars, notably the 100-LS.

''I don't want to be Porsche, I don't want to be the star (Mercedes), I don't want to be that other German manufacturer in Munich (BMW),'' Fisher says. ''I want to be Audi.''