In an audacious act of apparent reprisal, suspected black nationalist guerrillas last night gunned down the black police commander whose officers killed 11 political protesters on a soccer field in a black "homeland" three months ago, police said.

Three bomb explosions also rocked the port city of Durban last night, one of them bursting an oil pipeline near a refinery, setting fire to the oil and spilling it into the sea, the government said. No casualties were reported.

Although no organization has yet asserted responsibility for the attacks, observers here said they bore the marks of the outlawed African National Congress. They appeared to indicate an attempted retaliation by the black underground for the South African government's massive crackdown since the declaration of a state of emergency on June 12.

A car-bomb explosion on Durban's crowded beachfront on June 14 killed three young white women and injured 68 people, most of them white. The exiled ANC has said its underground agents may have been responsible for that attack.

The killing of the police officer, Brig. Andrew Molope, in the Winterveld squatter camp northwest of Pretoria where the killings took place on March 26 marked the first time in recent history that there has been a reprisal assassination of a senior official in South Africa.

Low-ranking black policemen have been the targets of many attacks in the nationwide civil unrest of the past two years in a general campaign against "collaborators" with the apartheid system.

A witness said gunmen fired several shots at the former police chief of the Winterveld district, in the nominally independent tribal "homeland" of Bophuthatswana, as he stepped out of his bullet-proof BMW to visit a friend in the squatter camp.

He was taken to a hospital in nearby Ga-Rankuwa township, but died before arriving there.

Molope, 41, a tall, powerfully built man who joined the South African police as a teen-ager and then got a top job in Bophuthatswana when it became nominally independent in 1977, was a hated figure in the Winterveld squatter camp because of his allegedly tyrannical behavior.

He gave the order to fire on a crowd of between 10,000 and 15,000 blacks gathered on a soccer field to demand the release of a large number of children who had been detained.

Molope told a commission of inquiry in the homeland two weeks ago that he had ordered the crowd to disperse after he established that they did not have permission to hold an outdoor meeting. When the crowd ignored the order, he instructed his men to fire tear gas, then live ammunition, at them, he testified.

"I realized that the lives of my men were in danger, that my life was, too, and I gave instructions that the police should use their firearms," he told the inquiry.

When the shooting stopped, 11 persons lay dead on the dusty field and another 30 were seriously wounded. Witnesses testified at the inquiry that they later saw Molope's men assaulting members of the crowd.

A month later Molope was promoted from colonel to brigadier and given a top job at police headquarters. "I am certain there is not a single person in Winterveld who considers me a threat," he testified. "I really work very well with the people." But he moved in fear of his life, always carrying a gun and traveling in his bullet-proof car.

A spokesman for the government's Bureau for Information said today that none of the bomb explosions in Durban was serious and that they had caused no deaths or injuries

One bomb exploded in a trash can on a street corner, blowing out a door and several windows of nearby shops. Another exploded near a chemical container in an industial area, causing slight damage.

The third bomb burst an oil pipeline in a feeder canal near a refinery that served several gasoline companies. Some of the oil caught fire and there was spillage into the sea, a bureau spokesman, Leon Mellett, said.

Mellett added that the fire had been brought under control, and the spillage was not serious. He said detergent to disperse the oil was being flown to Durban from Johannesburg.

The bureau reported one more unrest-related death today, bringing to 56 the number of people known to have died in violent incidents since the emergency was declared. This is slightly higher than the average of five deaths a day before the emergency, despite repeated government statements that the level of violence has declined substantially.

About 150 members of a church congregation who were arrested in the mixed-race township of Elsies River, near Cape Town, on June 16 were released today. Six were released earlier in the week, the bureau said. Thirty-three are still being held.

An estimated 3,000 persons have been detained under the emergency.