At a painstaking pace, a dozen new Volkswagens a day take warm-up laps around the six-mile assembly line in the nation's newest auto plant.

More like a turtle treadmill than the Rabbit Hutch that a bilingual sign proclaims the plant to be, the conveyer slowly accelerates toward its eventual output of 800 cars a day, 200,000 a year.

Mufflers from a Maremont Corp. factory in Louden, Tenn., are bolted onto floor panels stamped from American steel in West Virginia. Wheels made by Rockwell International in Brazil roll onto tires from several Akron plants and are stopped by Bendix brakes.

The worker who drives the newly built cars off the conveyer steers a wheel made in Detroit by Olsonite Corp., looks through a windshield that came from a Pennsauken, N.J., Combustion Engineering Co. glass factory and flips on a Motorola radio.

It will be several weeks before assembly line workers are adept enough to put together the 400 cars in eight hours the plant is designed to produce, and September before the second shift is added.

Although turning a 39-acre shell abandoned by Chrysler Corp. into a functioning factory in 18 months, as VW has done, is a major accomplishment, the success of the German auto maker's $250 million gamble on U.S. manufacturing still depends on what happens in the months ahead.

VW still is hiring workers to run the plant, still is looking for American manufacturers to make parts for it, and still is vulnerable to the international currency fluctuations that are the primary reason its share of the American auto market has plummeted from 5 percent to 2 1/2 percent in the past five years.

Back in the days when a Beetle cost $2,000, the German mark was worth about 25 cents. Now the mark is valued at 49 cents and $4,000 Rabbits - barely competitive with Detroit compacts in cost - face further price increases as the value of the dollar erodes.

To short-circuit that threat, VW came to America, but its American Volkswagens are still two-thirds German. That means not only that VW pays a 3 percent duty on imported parts - adding perhaps $75 to the price of its American Rabbits - but also that two-thirds of the car is still subject to the whims of international exchange rates.

The next goal of Volkswagen Manufacturing Corp. of America, the U.S. production company, is to reverse the ratio of imported to domestic components. Eventually the only major imported parts will be the engines, clutches, transmissions and drive train, the same parts VW sells to Chrysler Corp. for its Dodge Omni and Plymouth Horizon subcompacts.

At the same time, the company must increase the productivity of its plant, which is regarded as the most modern - and therefore the most costly - in the American auto business. At a dozen cars a day, the output of the Pennsylvania plant would be too expensive even for Porsche - the VW subsidiary that makes the $11,000 to $25,000 sports cars parked among the pickup trucks outside the rural Pennsylvania facility.

Within a year, the productivity of American workers will be as good as or better than that of VW's German assemblers, Toni Schmuecker, president of Volkswagenwerk A.G., the German parent company, predicted last week. And within a year, VWOA will reach another stage of growing up in America - negotiating a union contract with powerful United Auto Workers.

More than a few of the workers assembling the first Rabbits already already are wearing UAW t-shirts or union buttons. Roughly 87 percent of VW's 1,000 production workers have signed cards calling for union representation, said Ray Ross, the UAW's regional director.

Because VW still is hiring the 3,000 workers needed to staff the plant, the National Labor Relations Board cannot call a union representation election. Under NLRB rules, 30 percent of the employes in an expanding work force must be working before an election can be held. Ross says that cutoff point should be reached this month, so the UAW-backers can petition for a vote.

The UAW already has a contract with VW's other U.S. plant, a South Charleston, W. Va., stamping factory that VW bought from American Motors Corp. to make body parts. Taking American Morors' 300 unionized woekers as well as its plant, VW quickly negotiated a new contract that Ross said raised wages about $1 and hour over what AMC had been paying.

That success and the Pennsylvania plant's location in an area where the union tradition is strong among coal miners and steel workers have led UAW officials to talk confidently about organizing the plant, and to take a low-key approach.

Only one union organizer has worked the VW palnt, Ross noted. There has been "none of the usual organizing acitivty" because VW has thrown up no barriers against the union. "We have not passed out leaflets, we have not flayed the management, because there is no need to," said the veteran of nearly 30 years of UAW organizing.

The company is "strictly neutral" on the issue of union representation of its workers, reporters were told at the dedication by James McLernon, president of VWMOA.

McLernon refused during the press conference to specify the wages being paid to Westmoreland workers, but other officials later said the average wage for production workers is about $5.50 and hour. Under UAW contracts with General Motors Corp., the main classification of assembly workers earn $7.65 and hour, a UAW spokesman in Detroit said.

Saying wage rates were set so they would "not disrupt the local economy," McLernon said VW is not about to match Detroit's pay scales. "This plant could not exist if it started out at parity" with GM, Ford and Chrysler, he asserted.

That point was repeated by Richard Dauch, the former GM executive who was hired as vice president and general manufacturing manager of VWMOA, who provided details of VW's employe compenstion.

Dauch said VW workers get hospital, medical and dental insurance benefits "comparable" to UAW members - and "very generous" by local standards - but are not yet covered by pension plans. The UAW contracts contain a "30 and out" retirement program that gives workers pensions of more than $600 a month after 30 years. Explained Dauch, "These people just got hired, they aren't worrying about retirement."

Dauch said VW's decision to build the plant was based on the assumption that labor costs would not start out at the same level as Detroit. Because of the low productivity of workers who are building only a fraction of the number of cars they are capable of turning out, paying UAW wages is out of the question, he said. "You can't start a new company and pay the same wages as somebody who's been in business for 50 years."

Responded Ross, "I wouldn't fault him for saying that. I wouldn't expect him to say he expects to pay the Big Three rate. I wouldn't expect them to pay that." But after the plant is organized and a contract signed, "American VW emplayes should expect to receive the going rate of pay," he added.

Describing the public comments of VW executives as "posturing for the bargaining table," another UAW spokesman said, "My guess is we will wind up with something similiar to the Big Three pattern agreement."

Ross said initial contacts between VW and the union have been unusually harmonious, contrasting with the vigorous attempts by GM and Ford Motor Co. to keep the UAW out of new plants that have opened away from Detroit. "VW's conduct so far has been exemplary," he said.

While union-management relations at Volkswagen Westmoreland lack the "Strum and Drang" of most American organizing efforts they are also missing the "Mitbestimmung" that is the essential feature of German labor relations. The word translates as "codetermination." As the definition has evolved since the 1920s, it has come to mean that German workers play a role in determining company policy and in administering compamy affairs,a U.S. Labor Department specialist explained.

That role extends from "worker councils" in manufacturing plants, which have a voice in day-to-day operations and even must approve plans for layoffs, to the board of directors of Volkswagenwerk AG, where Eugen Loderer, president of the German metal workers union, I.G. Metall, sits as vice chairman of the board.

Will codetermination come to Westmoreland? "It's two different countries, tow different systems, two different cultures," Dauch said. "There's no need for it here."