JOHANNESBURG, South Africa (AP) _ The nation's largest black labor federation warned Monday that the detention of its president could provoke spontaneous protest strikes across South Africa.

In other developments:

-The government said eight more blacks were killed in unrest, raising the toll to 93 since the government declared a national state of emergency June 12. Three victims died in clashes Sunday between militants and supporters of moderate black Zulu leader Chief Mangosuthu Buthelezi in Soweto, Johannesburg's huge black township.

-Two bombs exploded before dawn on a pedestrian bridge over a freeway near Durban, bursting water pipes but hurting no one, the Bureau for Information said. It was the ninth bombing since the emergency.

-The government ordered the deportation of West German television correspondent Heinrich Buettgen, the fourth foreign journalist told to leave during the emergency.

The Congress of South Africa Trade Unions, which claims about 500,000 members, said the detention of its president Friday night was ''further proof of a direct and concerted assault on trade union freedom in South Africa.''

The federation noted that thousands of workers already had staged wildcat strikes at about 100 chain-store branches during the emergency to protest the seizure of union officials and shop stewards. The arrest without charge of the union chief ''could spark widespread and spontaneous worker reaction around the country,'' the congress said in a statement.

The name of the detained union leader, a longtime anti-apartheid campaigner, may not be disclosed under press restrictions imposed as part of the emergency proclamation.

The federation said detention of labor leaders would be discussed Tuesday at an executive committee meeting.

Hundreds of activists, including most of the 40 executive members, have been in hiding to evade detention.

The federation's general secretary, Jay Naidoo, said in a clandestine interview last week that the executive members would meet openly Tuesday, in a direct challenge to the white-led government to allow free union activity.

But spokesman Frank Meintjies said on Monday that the meeting site would not be disclosed, lest more arrests follow.

Reports from labor federations in Britain and Switzerland on Sunday said that Naidoo likely had been detained, but Meintjies said that Naidoo was free, but in hiding, and planned to attend the executive meeting.

Meintjies told The Associated Press the president was picked up at his home in Carltonville, a mining town west of Johannesburg. The union chief, the most senior labor leader jailed without trial during the emergency, is also vice president of the 250,000-member black National Union of Mineworkers.

The Labor Monitoring Group, an independent team of academics, said Saturday at least 923 union members were known to be in detention. It said 740 more workers were arrested while striking dairy plants to protest earlier detentions.

The Bureau for Information has said no union leaders were held for labor activities, but because of involvement in anti-government activities.

White business executives joined unions in asking that labor leaders be released, saying detentions and resulting strikes threaten chaos in industry.

Analysts have long described the emerging black trade union movement as potentially the most significant force for peaceful change in South Africa. Black unions were legalized in 1979 under reforms introduced by President P.W. Botha's government, and about 1 million blacks now are members of trade unions.

Black unions over the past two years increasingly entered the political arena. Twice in two months they endorsed one-day protest strikes that kept millions of blacks off the job.

The federation, launched in December with about 30 member unions, is affiliated to the United Democratic Front anti-apartheid coalition.

The information bureau said in a daily unrest summary that the latest violence was concentrated in Soweto and Tembisa, a township northeast of Johannesburg.

Militant youths hurled rocks and a gasoline bomb in attacking buses carrying home hundreds of Buthelezi supporters from a Soweto rally Sunday.

One driver, his clothes aflame, leaped from his bus and it ran into a crowd, killing two people.

Following buses also crashed, and 48 passengers were hurt, the bureau said. Thirty-six blacks remained hospitalized Monday.

Irate passengers stabbed one youth to death, and a black man was stoned to death by a crowd Sunday night, the bureau said.

It said two blacks were killed in Soweto Saturday night when security guards fired on youths attacking the home of a black councilor.

In Tembisa, a black man shot himself to death after he fired at a police patrol and police returned the fire, the bureau said. Also in Tembisa, a black policeman who was set afire Saturday died in a hospital.