JOHANNESBURG, South Africa (AP) _ A black auto workers union on strike at the General Motors plant in Port Elizabeth said Thursday that the company had changed its bargaining stance, and a company spokesman reported talks with the strikers had been constructive.

About 3,000 workers at the plant fear they will be fired when new owners take over. GM has said the new owners will be identified on Monday.

After two hours of negotiations Thursday, Fred Sauls, a spokesman for the National Automobile and Allied Workers Union said: ''There has been a move from the company. They seem to be seriously considering the situation.''

GM's industrial relations director, Bob McIlwaine, said talks would probably continue Friday. ''I think the discussions we had were constructive,'' he said.

The strike began Wednesday when the union's 2,000 members at the plant refused to work or leave until their demands were met. A smaller black union joined the auto workers, but a white union did not.

The workers are seeking severance pay from GM when it turns the plant over to the new owners; refunds of employee contributions to life insurance and pension plans; and two union members on the new board of directors.

General Motors, the biggest U.S. car maker, announced Oct. 19 that it was leaving South Africa. GM has lost money on its operations here and the union fears the new management may fire workers to reduce costs.

Bob White, the company's managing director in South Africa, addressed the employees Tuesday and said there was no indication they would lose their jobs under the new management.

McIlwaine said Thursday that White indicated he would relay the union's request for representation on the new board of directors. He would not say if there was progress on the other points.

Several hundred workers stayed overnight in the plant Wednesday. The rest returned Thursday but no one worked, GM and union spokesmen said. Very few workers stayed Thursday night, and Sauls said the union was recommending they all go home over the weekend.

General Motors obtained a court order late Wednesday that will let it fire striking workers Monday morning if the union does not prove by then that the strike is legal.