JOHANNESBURG, AUG. 29 (SATURDAY) -- The giant Anglo American Corp., hit hardest in a three-week-old strike by South Africa's black miners, and the National Union of Mineworkers ended nearly seven hours of negotiations early today after the company's dismissal of nearly a quarter of its work force in the dispute.

The two sides, both bruised in the strike, indicated that they had made some progress in an effort to break the prolonged deadlock over wages, the main issue in the often violent dispute, and scheduled a formal bargaining session for Sunday.

In a joint statement, itself a measure of progress, the company and the union said that their talks, which ended just after midnight, were intended to "explore avenues to reach a settlement of the dispute and an end to the strike.

"The talks were frank, and certain undertakings were discussed," the statement said. "The contents of the discussions will be referred to members of the National Union of Mineworkers and the principals of Anglo American."

Neither company nor union officials would elaborate on the statement.

A senior mining industry source commented later that there were still "some big stumbling blocks" to an agreement and that the negotiations Sunday between the mineworkers and the Chamber of Mines, the employers' group to which Anglo American belongs, would undoubtedly be tough.

The negotiations apparently were resumed at the union's initiative yesterday morning after Anglo American stepped up its mass dismissals of strikers, who had earlier turned down a take-it-or-leave-it offer from the mining companies.

Anglo American, which had already fired almost 10,000 strikers, dismissed more than 20,000 Thursday and nearly 20,000 others yesterday when the miners refused to return to work as ordered. About 10,000 more strikers have been dismissed by other mining companies in the last week.

In Cape Town, a senior Cabinet minister warned of possible government intervention if the strike continued and threatened the country's economic stability.