JOHANNESBURG -- With half of South Africa's black miners on strike, sharply cutting the economically vital production of gold and coal, Cyril Ramaphosa has emerged as the country's strongest labor leader and a political heavyweight as well.

For five years, Ramaphosa, 34, general secretary of the National Union of Mineworkers, has been preparing for the present showdown with South Africa's wealthy mining companies, knowing that it would be a test of strength for the whole black labor movement as well as for the broader fight against apartheid.

"This is the big one," Ramaphosa said as more than 300,000 miners began the strike two weeks ago. "If we win this strike, it is going to be a significant motivation for all other workers to continue with their own struggle for a living wage. If we lose, it will have a devastating effect."

Ramaphosa also acknowledged that the strike is "about a lot more than wages" and that if the union wins, the victory will have major political implications.

"To the government, we represent a constituency that is part and parcel of the liberation movement in this country," he said. "There is a lot of fear and trepidation in government, I think, about the outcome."

A substantial union victory, confirming the mineworkers' fast-growing strength in the country's most important industry, would encourage other black labor unions and their allies in the United Democratic Front, a coalition of antiapartheid groups, which has been hit hard in the past year by the government's state of emergency.

"With so many groups forced almost underground by the state of emergency, unions increasingly are taking the lead in the {antiapartheid} struggle," a United Democratic Front official said the other day. "With so many of our leaders detained, trade union men like Cyril Ramaphosa are moving to the fore."

Ramaphosa, a lawyer, came to the labor movement from politics, and he belongs to the increasingly influential group of young black leaders, most of them now in their mid-thirties, who were first drawn into the struggle by the late "black consciousness" leader Steve Biko.

Biko, who died in police custody in 1977 at age 31, had infused many young blacks with a new pride in themselves. By founding the South African Students Organization and Black People's Convention, he had encouraged them to unite for the first time in more than a decade to fight apartheid and throw off their "shackles of servitude."

In the 1970s, Ramaphosa was a branch chairman of the South African Students Organization and an active member of the Black People's Convention, both of which were later outlawed by the government. He was detained under the country's security laws twice without charge, once for 11 months and later for six months, because of his political activities.

When Ramaphosa finished his studies, in 1981, he joined the Council of Unions of South Africa as a legal adviser, and he was given the task of organizing the country's 600,000 black miners, less than 1 percent of whom belonged to any union.

The only previous black mining union of any size, the African Mine Workers Union, was crushed in 1946, when 70,000 miners went on strike for higher wages but were forced back to work at bayonet point. Police had similarly broken a strike by 71,000 black miners in 1920.

Ramaphosa went from mine to mine, attempting to mobilize workers from half a dozen ethnic groups with varying political outlooks. Although often harassed by mine managers, he gradually built up the mineworkers' membership -- it now has more than 320,000 -- and then won recognition for the union from the Chamber of Mines, which groups South Africa's six major mining companies.

Company negotiators describe Ramaphosa as "sophisticated," "impressive," "hard-working" and "very, very able," although they do not like to say so too often or too publicly. They are annoyed, however, by what they see as his commitment to socialism, including nationalization of the country's mines, and by his calls overseas for the withdrawal of foreign companies from South Africa.

Over the years, Ramaphosa's political views have shifted. Like many of his generation, he has moved from the "ourselves alone" racial exclusivity of black consciousness. In doing so, he took the mineworkers out of the all-black Council of Unions of South Africa to establish the nonracial Congress of South African Trade Unions.

As head of the country's largest black union, Ramaphosa also has been instrumental in forging an alliance between the union federation and the United Democratic Front and in winning formal acceptance by them of the 1955 Freedom Charter, the basic manifesto of the outlawed African National Congress.

In 1984, he led the mineworkers on their first legal strike -- a brief, confused and bloody affair in which at least 10 miners died. There was a second strike in 1985, again over wages, and an abortive work stoppage last year.

Each was an attempt to develop the union's bargaining strength with the giant mining companies, to expand its membership and increasingly to alter the balance of power in the mining industry.

The current strike, seeking a 30 percent pay increase, was planned to avoid the mistakes made in earlier years and to force the mining companies to negotiate a wage agreement rather than simply announce what they will give the workers.

"They still do not take us seriously," Ramaphosa said at the outset of the strike. "They have been patronizing -- more than that, arrogant, actually. . . . But they will pay for their arrogance."

He had predicted that 200,000 of the union's members would go on strike at 56 targeted gold and coal mines and that perhaps 100,000 other miners would join. The union later claimed that more than 340,000 miners were on strike, but the Chamber of Mines put the figure at a maximum of 230,000 and said it was decreasing.

"We have a major crisis every day, often two and sometimes three," Ramaphosa said as the second week of the strike drew to a close, "but the strike is still solid."

Ramaphosa's long-term goals include sweeping changes in the whole mining industry. An immediate goal is ending the migrant labor system, which forces miners to live in fenced, guarded hostels without their families for most of the year.

"We want to get rid of this system," he said. "It is inhuman to expect anyone to live without his family for 11 months of the year.