JOHANNESBURG, AUG. 27 -- More than 22,000 black miners were fired today as South Africa's major mining companies tried to break a strike that has halted work at a third of the country's gold and coal mines for nearly three weeks.

Anglo American Corp., hit hardest by the strike, said that it dismissed more than 20,000 miners at five gold mines and four collieries when they refused to return to work. The company warned that it would fire another 20,000 over the weekend if they also stay out.

Similar moves appear to be planned by two other companies, General Mining Union Corp. and Johannesburg Consolidated Investments Co., and the number of dismissed workers could total more than 80,000 within a few days.

The Congress of South African Trade Unions warned of a nationwide general strike in support of the miners. Such an action would intensify the political crisis and perhaps bring government intervention.

Jay Naidoo, general secretary of the 712,000-member congress, declared, "Black workers in this country have very few weapons, but withdrawal of our labor is one of them. A general strike is not a last resort -- it is one of the weapons that we have."

More than 300,000 of South Africa's 600,000 black miners have been on strike since Aug. 9 to support their demands for higher pay, improved fringe benefits and better working conditions.

The companies have proposed compromises on many of the miners' demands, but they have refused to increase their offers on wages, the main issue.

The mining companies have already increased pay 15 to 23 percent. The union had been seeking 30 percent, but this week reduced its demand to 27 percent in hope of a company counteroffer.

Members of the National Union of Mineworkers voted overwhelmingly yesterday to reject an industry offer that included higher death benefits and vacation pay because it did not include a new wage proposal.

Although Anglo American had said there was a "substantial return" to work by the miners this week, it acknowledged that more than 80 percent of the workers had accepted dismissal rather than go back to work.

Among those dismissed today were 3,000 miners who conducted an 18-hour sit-in inside one of Anglo American's gold mines west of Johannesburg. They were protesting what they said was the use of force by mine security guards to make them go underground to work.

Most of the men came to the surface late today and were handed severance pay and put on buses to their homes in remote rural areas. Anglo American confirmed the sit-in but denied that force was used to make miners go to work.

Anglo American had earlier cited "an urgent need to resume mining operations" amid speculation that it had borne more than half of the loss from the strike. The walkout is estimated to have cost the industry more than $100 million in pretax profits.

South African labor law permits recognized black unions to strike, , but it also allows the companies to discipline striking workers by locking them out and firing them if they do not return to work when ordered.

Naidoo said 350 top officials of union congress affiliates met this week and agreed to support the mine workers, the largest of its constituent unions, with "solidarity actions."

A general strike, as suggested by Naidoo, would probably be illegal under the 14-month-old state of emergency in South Africa, but the labor federation has organized a number of "stay-aways" to protest government policies over the past year without prosecution.

"Workers are angry that their comrades on the mines, who are the main wealth producers in the country, are being shot at, tear-gassed, starved, arrested and detained," Naidoo said. He said the congress would try to discourage the recruitment of replacement workers from neighboring countries and in rural areas in South Africa, and would mount an international campaign against purchase of South African gold and coal.