DETROIT, SEPT. 13 -- Negotiations between the United Auto Workers and General Motors Corp. today appeared headed toward agreement on a new three-year contract the union hopes will provide job security for its members into the next century.

Although negotiators still had tough issues to resolve with little more than 24 hours to go before the contract expires at 12:01 a.m. Saturday, both sides said they were optimistic an agreement could be reached by the deadline.

Perhaps the biggest sign of optimism was the fact that the UAW leadership has called a Monday meeting here of its 300-member GM bargaining council. The council must approve any agreement before it can be sent to the membership for ratification, and it is usually not summoned here unless the leadership believes an agreement will be forthcoming.

In addition, the UAW executive board is scheduled to meet Saturday.

The key to any settlement is the job-security provision for a union that has lost more members since the beginning of the 1980s than it currently has employed at GM. The goal is to guarantee the jobs of the 289,000 active union members at the company while giving some hope of future employment to the 30,000 UAW members on indefinite layoff at GM.

Politically, however, the biggest issue for the union may be its insistence on some type of job-security formula that will guarantee a minimum employment level for UAW members in the future.

Negotiators have been discussing formulas for job levels should the domestic carmakers gain more market share. Although details of any job-security agreement were being closely guarded by both the company and the union, UAW sources indicated the security plan was beginning to take some shape at the bargaining table. "You don't need to use a telescope to see it," a UAW source said. "You can use binoculars now." He emphasized there was still quite a ways to go before an agreement could be reached.

The UAW picked GM as a target company for this year's negotiations because, unlike Ford and Chrysler, the company manufactures in-house a majority of the parts it uses to build cars and trucks. GM has insisted from the start that it must be allowed to pare down its work force if it is going to continue to manufacture the majority of the component parts it uses.

Whatever agreement the union reaches with GM, it will serve as a pattern for bargaining with the other two companies.

Other major economic issues on the GM table such as pensions, wages and health care have basically been settled.