General Motors Corp.'s highly touted Saturn compact car is finally under way after nearly eight years and $3 billion in the making. But the real question is which way is it headed?

One glance at the car magazine racks shows headlines that read "Saturn Launched" or "We Have Liftoff," expounding on the spacy, car-of-the-future theme that former GM Chairman Roger Smith played up during most of the 1980s.But GM's ambitious project to drive rings around what has become a very formidable group of Japanese automakers is headed for even more nebulous territory, one where cars either live or die - the sales showroom.

GM repeatedly has stressed that production techniques used at Saturn's massive $1.9 billion manufacturing complex in Spring Hill, Tenn., are what will give these cars a high orbit when they go on sale Oct. 25, initially in the South and West.

They mark the first high-volume use of bodies made from both steel and recyclable plastic, for instance. This means special production processes, but the payoff is that styling changes can be made quicker to meet ever-changing buyer tastes.

Its fuel-efficient, four-cylinder aluminum engines are cast using a unique lost foam process, which allows greater design flexibility and more integration of components into a single part. Saturn also is the first U.S. automaker to produce manual and automatic transaxles on the same line.

Without minimizing such novel advances, Saturn's success still will be ultimately gauged where the rubber meets the road.

Obviously, a large part of that success will depend on whether buyers perceive enough value to be swayed from other brands and give GM another chance after watching the giant carmaker repeatedly fail at building a small car during the last three decades - the Chevrolet Corvair, Chevrolet Vega and Pontiac Fiero.

By that token, GM is taking little chance with Saturn's debut.

Last week GM surprised some analysts by announcing a base price of $7,995 for the most inexpensive Saturn. That is about $1,000 below some projections, although there had been rumors of an entry price in that range.

At the top end is the Saturn SC sports coupe, which starts at $11,775.- Two other sedans are sandwiched in between: the Saturn SL-1 sedan ($8,595) and Saturn SL-2 Sports Touring Sedan ($10,295).

All have an AM-FM stereo, rear window defogger, folding rear seat, adjustable steering column and stainless steel exhaust system. While anti-lock brakes are offered at extra cost, air bags will not be on board until 1994 at the earliest.

But once equipped with popular options like air conditioning, automatic transaxle and tape cassette, Saturns will be selling in the $10,000-$15,000 range as projected.

That means GM's clean sheet approach to building a small car faces stiff competition not only from the Honda Civic, Toyota Corolla and Ford Escort, but from the Geo Prizm and Storm imports marketed by GM's own Chevrolet division.

It also means that other GM divisions, like Pontiac, Oldsmobile and Buick, could lose sales of their smaller cars to Saturn, although Pontiac General Manager John Middlebrook insists Saturn will "break the import barrier" and prompt buyers to consider all GM cars once again.

A decision also was made to keep GM's name and logo out of Saturn's advertising, possibly to minimize any distaste GM car owners may have had for the automaker's poorly built products during the 1980s. It is not clear whether GM or Saturn made that call.

Still, it is a safe bet GM will be sure to ring in and share the spotlight should Saturn's first report card be favorable.

Saturn now has the capacity to build about 240,000 cars a year, although output is expected to be about half that until mid-1991.

Buyers will be voting with their pocketbooks from this month forward, with recent geopolitical events playing into GM's hand for once, given higher fuel prices that may boost sales of fuel-efficent cars like Saturn.

But it will be a year or two before GM's most ambitious small car project is declared a success or failure.