United Auto Workers union leaders today approved a labor contract that gives their members an unprecedented management role at General Motors Corp.'s new Saturn automobile plant.

The agreement also breaks new ground by eliminating time clocks and giving production workers an annual salary. It guarantees "permanent job security" for at least 80 percent of the UAW-represented workers at the Saturn manufacturing complex, and paves the way for the long-awaited announcement by GM of where the plant will be located.

In return for sharing management power, the union agreed to new work rules to make the Saturn cars more competitive with Japanese small cars in the U.S. market. The rules give management more flexibility in assigning workers to many different jobs.

UAW Vice President Donald F. Ephlin, the union's chief negotiator with GM, called the agreement "a milestone and leap forward" in labor-management relations.

"The union will be represented at all levels of the organization . . . and we'll participate in all the decisions at all levels," the union's outline of the agreement said.

That means the union will have the right to veto any decision affecting the direction of the Saturn corporation, UAW President Owen Bieber said. "The union will be a full partner in all decisions -- from the shop floor to the top-level Saturn Strategic Advisory Committee," Bieber said. The committee, the equivalent of GM's executive board, will make plans on matters affecting all aspects of Saturn operations.

"No decision can be made, no action can be taken without agreement by the workers. That is a degree of co-determination never before achieved in U.S. collective bargaining," Bieber said.

The location of the plant has been the subject of intense media speculation and regional bidding since Jan. 8, when GM Chairman Roger B. Smith unveiled the creation of Saturn Corp.

Union sources said that GM will build the $3.5 billion complex in Spring Hill, Tenn., about 30 miles south of Nashville and 35 miles from Nissan Motor Co.'s nonunion truck and auto plant at Smyrna, Tenn.

Top UAW and GM officials refused to confirm or deny those reports. In Washington, however, Tennessee's two senators, Albert Gore Jr. and Jim Sasser, said the union approval today eliminated any doubt that their state had won the plant.

GM, which wanted to have a Saturn labor agreement in place before announcing the site, is expected to announce its choice early next week.

Putting Saturn in Tennessee, close to Nissan's plant, is strategically important for both GM and the UAW, several union sources said.

GM would gain the advantage of trying its "clean-sheet" approach to car manufacturing outside the Midwest -- the nation's traditional auto-making corridor. The UAW would "get a license to go after Nissan" by having a high-profile operation very near the Japanese-owned plant, one source said.

"I hope that wherever the plant is located, it will be a showcase and it will be fully competitive with Nissan," said the UAW's Ephlin. He said that his comment was not to be taken as confirmation of the Tennessee report.

"The important thing is that we can demonstrate that we can build small cars competitively in the United States in what is not only a union plant, but in what will be the most union-involved plant in America," Ephlin said. "I would hope that would make an impression on the Nissan workers."

Switching from hourly wage to salary for production workers creates what Ephlin calls "consistency of treatment among all those involved in the venture," and gives union members the same prestige of other employes.

The contract approved today initially will cover 6,000 Saturn production workers, most of whom will be hired from current UAW-GM membership rolls. The starting base wage rate for those workers will amount to the equivalent of $13.45 per hour for assembly employes and $15.49 per hour for skilled trades workers. Those figures are comparable to wages at other plants.

Later those wages will be lowered to 80 percent of competitive base rates, but workers will be able to make up the difference by earning production and other bonuses.

The Saturn Corp. is expected to begin by 1990 and to produce up to 500,000 subcompact cars a year.

In an interview earlier this year with The Washington Post, Alfred S. Warren Jr., GM's vice president for industrial relations, said that a major objective of Saturn was to make the UAW a "full partner" in manufacturing and other corporate operations.

"We want to have a greater flow of information with the union at all levels," Warren said. "I think that's healthy. The UAW is an integral part of our business, and I think that they ought to be treated that way," Warren said.

Warren also said that he did not believe the UAW "can afford to let Nissan" and Honda Motor Co. Ltd., in Marysville, Ohio, "go unorganized."

"All Japan is watching two things here, Honda and Nissan," Warren said. "If they continue without a union, other Japanese manufacturers might get the idea that they too can work in the United States without a union," Warren said.

Bieber said that the Saturn contract, despite its radical nature, is written in such a way to prevent GM from transferring some of Saturn's favorable work rules to GM's big car facilities.

Saturn specifically is designed to help GM become competitive in the hotly contested small car end of the U.S. auto market, Bieber said. U.S. car manufacturers are taking an overall beating in that segment, largely because Japanese car companies are producing comparable models at $2,000 per car less than that of their American rivals.

Saturn is "a special project designed to maintain small car production in the United States," the UAW executive board said in a note accompanying the approved contract.

The agreement "does not set precedent regarding the union's policy at any other facility including those at General Motors," the note said.

The contract approved today initially will cover 6,000 Saturn production workers, most of whom will be hired from current UAW-GM membership rolls.