What was going on when I was born?

The South African police shot and killed six black protesters, detained at least 18 prominent political activists and rounded up 500 black schoolchildren today. The police said the children were boycotting classes. On Thursday, 300 children were seized under similar circumtances in a police effort to force children to halt the boycotts. Township residents said many of the children were under 13 years old.

Brushing aside ''technicalities,'' a state appellate court yesterday ordered Assemblyman Herman D. Farrell Jr. reinstated to the Sept. 10 Democratic primary ballot for mayor. It also reinstated four candidates for City Council president. Mr. Farrell, the four Council president candidates and several candidates for other offices had been ordered off the ballot by a state judge because of numerical errors in the cover sheets of their nominating petitions. Council President Carol Bellamy, who had challenged Mr. Farrell's petitions, said late last night that she would drop her effort to force Mr. Farrell off the ballot.

The large leak of toxic gas from a Union Carbide factory near here two weeks ago resulted from violations of plant procedures and other failures left uncorrected by plant workers for up to 10 days before the accident, company officials said today. They accepted full blame for the incident. In a news conference and in subsequent interviews characterized by strong self-blame, top corporate and plant officials pinned the fault for the leak at its factory at Institute directly on failures of management, operations and equipment solely under the company's control. High-pressure alarms were repeatedly shut off and ignored. A high-temperature alarm was out service. A level indicator in the tank that leaked and was known to be broken was not fixed. Meanwhile, the unit's computer, which silently recorded the rising problems for days, was never asked for the information by operators, the company's chief investigator said in an interview. #2 Breathing Masks for 6 People Company officials painted a grim picture of the chemical unit's six operators huddled together in the control room on the morning of the accident, enveloped by a thick cloud of toxic gas and forced to share the only two breathing devices in the room.

Once forced to rely on others to read, write or speak for them, about 20,000 people across the country are now using specially adapted personal computers to help make up for their disabilities. The technology has the potential to allow about four million Americans to compete in mainstream employment and education, according to experts in the field. For the visually impaired, a voice synthesizer can be attached to a computer to read words that appear on a video display terminal. A similar device can be programmed to speak for people who cannot talk. Software can translate the text appearing on a computer screen into printed Braille. The same text can be displayed on a VersaBraille, which has plastic pins that can be raised and lowered to form a line of Braille.

New York City's reservoir levels are expected to fall steadily over the next two months to as low as 30 percent of capacity, water officials said yesterday. Unless exceptional rainstorms produce runoffs, most rainfall will be absorbed by plants and dry ground, and will not help fill the reservoirs, the officials said. But for now, they said, there are no plans for new restrictions on consumption. They expressed hope that existing curbs and increased voluntary measures would reduce consumption enough. Waiting for a Turnaround The officials said they expected the reservoir levels to reach their low point in November, but a spokesman for the city's Department of Environmental Protection said there was no way to predict when the refilling of the reservoirs would begin.

British Airways said today that it had not been told of the results of an American investigation into the reliability of aircraft engines of the type implicated in an airliner fire in northern England. Fifty-four people were killed Thursday when a Boeing 737 operated by a British Airways subsidiary burst into flames as it began to take off in Manchester. Officials said an engine exploded as the plane neared takeoff speed, sending engine parts flying through the air. One fragment is believed to have severed a fuel line, igniting a kerosene fire.

A top-ranking official in West Germany's counterintelligence agency was reported today to have defected to East Germany. Officials here agreed that the defection of the official, Hans Joachim Tiedge, had jeopardized Western espionage operations and confronted Chancellor Helmut Kohl's Government with a major scandal. A hint of the possible repercussions came in an East German report today that suggested that 168 West German agents had been apprehended in the last year and a half. No Official NATO Comment The North Atlantic Treaty Organization had no official comment, but NATO intelligence experts in Brussels said the defection was a major blow to allied counterintelligence. In Washington, the State Department said the United States would consult with West Germany to determine the damage to their mutual security interests.

Political leaders of the Nicaraguan rebels have decided to spend time in the field talking with rebel commanders and fighters in an effort to halt what they acknowledge are summary executions and other human rights abuses, according to one of the leaders. The rebel political leader, Arturo Cruz, said ''certain accords'' about human rights were reached at a meeting last week in Honduras of the leaders of the United Nicaraguan Opposition, a new rebel umbrella group known as UNO. The rebels, whom the Reagan Administration refers to as ''freedom fighters,'' are to receive $27 million in nonmilitary aid under legislation approved by Congress in June. Several international human rights organizations have reported that the insurgents carried out widespread violations of human rights, including executions, rapes and torture.

An unmanned United States spy plane crashed into a mountain in eastern El Salvador today while gathering information on rebel movements for the Salvadoran military, a United States Embassy spokesman said. The small, remote-controlled drone reportedly slammed into a mountain near the town of San Carlos, 75 miles east of here. The spokesman said he did not rule out the possibility that it had been shot down by guerrillas.

Relations between the political and military wings of the Salvadoran rebel coalition have grown more tense in recent months, but the continued alliance between the leftist parties and armed guerrilla groups is not threatened, according to senior rebel political officials. The political leaders have criticized the guerrillas for kidnapping mayors, burning their offices and mistreating civilians. The debate within the rebel movement on the treatment of civilians grew especially heated, according to several rebel officials, after a guerrilla squad killed four American marines and nine civilians in San Salvador two months ago.

The rector of the University of San Carlos here is out to set an unusual record. He would like to be the first head of the school to finish a term in office since 1978. But the rector, Dr. Eduardo Meyer Maldonado, is aware that it may not be an easy task. Overseeing Guatemala's national university has proved to be a high-risk occupation of late, as political violence, much of it Government-directed, has swept the country.

A Syrian-sponsored cease-fire went into effect today, bringing a pause - however temporary - in one of the worst rounds of factional fighting here in years. Since a sudden surge of car bombings and artillery barrages began 11 days ago, 282 people have been reported killed and 862 wounded. Authorities here say the toll is remarkably high for this country, where people have learned to duck into basements and sandbagged shelters at the first sign of trouble.