Thirty-four black unions, newly joined in the biggest labor federation in South Africa, committed themselves today to an active role in black politics and the struggle against apartheid.

Elijah Barayi, the president of the Congress of South African Trade Unions, challenged President Pieter W. Botha at an inaugural rally today to lift the state of emergency, abolish laws that require blacks to carry passes, and withdraw troops from black townships.

"We are going to give a lead. COSATU is going to govern this country," Barayi said.

At the rally, the previously apolitical unions also declared their support for disinvestment. Barayi deplored the fact that the U.S. and British governments were opposing that campaign against South Africa.

"They tell us they are against disinvestment because the black people would starve, but black people have been starving here since the first white settlers arrived in 1652," Barayi said.

The formation of the new union federation this weekend, just six years after black trade unionism was legalized, has been widely described as a milestone event that could change South Africa's economic and political fabric.

Putting the government on notice to abolish the pass laws, Barayi said: "We give Botha six months to abolish these laws, which stop us from working where we want to and doing the work we want to do. If he doesn't do it, then we will take all the passes of the black people and burn them."

This would repeat a defiance campaign in 1960, when thousands of blacks burned their passes at the call of the main black political parties, the African National Congress and the Pan-Africanist Congress, and presented themselves at police stations for arrest.

The action resulted in the Sharpeville massacre, when police opened fire on a crowd. In the international outcry that followed, the government banned both parties, and they have remained outlawed ever since.

Another big rally of blacks in Port Elizabeth agreed today to suspend a crippling boycott of white-owned shops in that city, but warned that if Nelson Mandela and other imprisoned black leaders were not released by April, and outlawed black political movements were not legalized, the boycott would resume.

In another development, 186 of the largest American companies operating in South Africa sent a memorandum to the government attacking the country's racially segregated education system and calling for its abolition. The memorandum was the second in two weeks.

The new federation's member unions, with a joint membership of about 500,000, are considered the best organized in the fledgling black labor movement and span the vital mining, metal, food, retailing and transportation industries.

This puts the federation in a position to back its demands for political reforms with a range of strikes that could paralyze the South African economy.

"With the economy already reeling from the impact of the township unrest and increasing pressure for international sanctions, this additional black muscle poses a direct challenge to the Botha government," said Johan Maree, a specialist in labor affairs at Cape Town University.

When black unionism was first allowed, most of the new unions decided to avoid politics. Although they declared their rejection of apartheid, they feared that they would be crushed in their early stages under South Africa's stringent security laws if they became politically active in opposing it. They decided to concentrate first on building up their membership.

But they have come under increasing pressure to play a more active role over the past year, as unrest in the black townships and violent clashes with riot police have radicalized many of their members.

The unrest also provided the catalyst for unification, which had been the subject of intermittent negotiations among the unions for nearly four years.

The radicalism was reflected at today's rally, at which the federation's leaders delivered fiery political speeches and about 10,000 unionists jogged around a sports stadium with colorful banners, singing freedom songs and chanting black nationalist slogans.

It was like the big political rallies that have been the focal events of black activism in the townships, but police watched from a discreet distance today, as if sensing that intervention could trigger a wave of retaliatory action that would damage the South African economy further.

In a display of the muscle the new union movement apparently feels it has, the 60-year-old Barayi wagged a finger at the watching police contingent and shouted: "I want to tell you that you will not arrest one soul at this meeting today. If you have come to provoke trouble, then you will get what you are asking for."

Barayi said the state of emergency must be lifted because it was inflaming the violence in the townships. His other challenges included demands for abandoning the policy of separate tribal "homelands" for blacks, "liberating" black women, and lifting the ban on the activist Council of South African Students.

Finally, to cheers from the crowd, he called on Botha to resign as president and "make way for the real leader of the people, Nelson Mandela," imprisoned leader of the banned African National Congress.

In an interview afterward, Barayi said: "The message is, we are going on the offensive."