JOHANNESBURG, JULY 15 -- The president of South Africa's largest trade union federation vowed today that blacks would seize control of South Africa and "bury" President Pieter W. Botha.

Speaking to a cheering convention of 1,400 delegates to the Congress of South African Trade Unions, Elijah Barayi said, "I'm here to bury P.W. Botha, not to praise him." He warned the government that labor unions would lead the revolutionary overthrow of the government.

The union convention -- the biggest gathering of black workers ever held in South Africa -- began as 200,000 black mine workers poised to shut down 27 gold mines and 18 collieries following a breakdown in wage negotiations with the employers' Chamber of Mines.

With much of the leadership of nonparliamentary opposition groups either under detention or driven underground by the 13-month-old emergency decree, black trade unions recently have moved to the forefront of the antiapartheid movement. At the same time, government officials have threatened to crack down on the politicization of the unions.

In a militant speech that reflected the preeminence of the black trade union movement and its rapid emergence as a leading force in the campaign against apartheid, Barayi said: "We produce the wealth of South Africa, yet we are the victims of a brutal and exploitative system of apartheid and capitalism."

Delegates responded by shouting freedom slogans as Barayi declared, "Victory or death, we shall win!"

The convention hall at the University of the Witwatersrand in downtown Johannesburg was festooned with banners reading, "One union, one congress, nonracialism, one industry, worker control."

Despite restrictions against meetings that advocate the overthrow of the government, there was no evidence of a police presence on the campus.

Barayi, a former gold mine worker, told cheering delegates, "Some say that this intransigent government will never hand power over to the black majority. Well, the black majority will have to seize power from this intransigent government.

"I know that by saying this, the Botha regime will one day lock me up, but let them do so," he added.

Signaling the convention's stated intention to officially adopt the Freedom Charter of the outlawed African National Congress -- the 1955 manifesto for ending racial separation and white minority rule -- Barayi declared, "There can be no freedom in this country unless the African National Congress is involved."

The trade union federation already has been the target of several police raids, and on May 6 two powerful bombs exploded in the basement of its Johannesburg headquarters. The federation blamed security police for the bombing.

Barayi sought to dispel speculation in the press here that the federation is softening its support of sanctions and disinvestment as forms of pressure on the government. "We support all forms of pressure against apartheid. Our resolution calls for increased pressure, including sanctions and disinvestment," he declared.

A senior official of the United Democratic Front emerged from hiding to tell the convention delegates that trade unions had become the most powerful antiapartheid force in South Africa.

Murphy Morobe, the front's publicity secretary, who has been sought by police since the imposition of a state of emergency on June 12, 1986, rejected the possibility of any talks between the government and his organization.