The last time his friends saw Matthew Goniwe alive, the former schoolteacher was climbing into his tan Honda sedan in Port Elizabeth Thursday night three weeks ago with three other black activists.

They were heading for Goniwe's home in this small country town 120 miles away. But they never made it.

Police found the car the next day parked behind a sand dune off the highway to Cradock. During the next four days they found four charred and mutilated corpses.

The mysterious death of Matthew Goniwe and his three companions has triggered new charges that right-wing death squads, possibly with government sanction, are operating in South Africa.

It also has given the country's freedom movement a new martyr in the struggle for black majority rule. The funeral of Goniwe and his colleagues, scheduled for Saturday, is expected to draw thousands of mourners to this remote town.

The United Democratic Front, one of the country's main opposition movements, contends that 27 of its members have disappeared since March and that six others, including Goniwe and his three companions, have vanished and subsequently been found dead. The families of three missing activists, officials of the Port Elizabeth Black Civic Organization, petitioned a local court this week to force the police to produce the men and have filed affidavits from witnesses who say they saw the three in police custody after they disappeared on May 8.

The discovery of the bodies of Goniwe and his friends has led the government to take the unusual step of denying that it had any role in the slayings. A statement issued two weeks ago called charges of state involvement "callous insinuations," and suggested that the four may have been victims of "the internecine power struggle between opposing radical organizations that have claimed many lives and resulted in untold damage."

But the statement has done little to convince people here that Matthew Goniwe's death was not sanctioned by someone in authority.

"We are not able to prove it," said Derrick Swartz, the front's spokesman in Port Elizabeth, "but the overwhelming view in the UDF and the community is that the authorities, in particular the South African police, had some connection with this thing."

Port Elizabeth police are investigating the killings, and the government has offered a $500 reward for information on the killers. But Nyameka Goniwe, Matthew Goniwe's wife who is left to raise two small children alone, said police have yet to question her about the case. Officers of the Port Elizabeth Murder and Robbery Unit, who are conducting the probe, were not available for comment today.

The chief victim was considered one of this country's most effective political organizers. Matthew Goniwe worked the dusty backroads and remote plateaus of this sheep-farming region, preaching defiance and assertiveness to blacks who for generations had known mostly the politics of deference and submission. More than anyone else, he is credited with inspiring a new mood of resistance in these sleepy, racially segregated communities.

"Matthew had incredible stature," said Swartz. "We can't even begin to calculate the loss to our rural organizing. For us he was dynamite."

Goniwe was born here, the son of an illiterate domestic servant and an itinerant firewood merchant. He spent four years in prison in the nearby black homeland of Transkei for subversive acts including possessing outlawed books on Marxism. While in prison he earned a university degree.

He came back to Cradock in 1983 to teach science and mathematics. But popular discontent over high rents in the overcrowded black township of Ilingelihle, where he lived, led him to organize a civic organization that became known as Cradora. "Life can be lousy in the townships, the lack of facilities, the frustration," Goniwe's wife recalled in an interview today. "Matthew was a brave man. The others were enthusiastic, but he had the know-how."

The white authorities quickly identified Goniwe as an unwelcome agitator and arranged his transfer to a school in a township 100 miles away. When he refused to go, they fired him, a move that triggered a 15-month boycott of classes by local students.

Political violence followed. When police banned all Cradora meetings, students held their own meeting in defiance, which police broke up with tear gas and clubs. Rioting students rampaged through the township, after which Goniwe and three fellow community leaders were detained. They were held six months without trial in the same prison near Cape Town where black resistance leader Nelson Mandela is serving a life term.

Goniwe's wife said prison was only one form of harassment. She said police regularly tailed their car, tapped their phone and tampered with their mail. She also said she witnessed an incident in February 1984 during which a white security police officer forced Goniwe off the road, dragged him from his car by the shirt collar and pointed a gun at him.

"He kept saying, 'I'll kill you,' " said Nyameka Goniwe of the policeman. "They had no reason to stop Matthew. It was just sheer humiliation."

Gladwell Macaula, the president of Cradora, said police were looking for evidence to incriminate Goniwe. He said he was offered money last year if he would make a statement implicating Goniwe and fellow teacher Fort Calata in local violence. Macaula said he refused.

After Goniwe was released last September, school officials still refused to reinstate him. Students burned the houses of black township council members and policemen considered sellouts to the white administration. Four persons were killed in various bouts of rioting, including one policeman. The entire township council resigned in January.

In April, students agreed to return to classes, and officials said they were nearing agreement to reinstate Goniwe to his teaching job. Meanwhile, he had been working as a rural organizer for the UDF and attending weekly meetings. It was after one such meeting that he and his colleagues, including Calata, vanished.

His wife said Matthew Goniwe knew his life was in danger and that he was extremely careful. She said Goniwe avoided the black townships of Port Elizabeth so as not to get caught up in the factional violence there between the UDF and members of the rival Azanian People's Organization. When they left that night last month, Goniwe and his colleagues told their friends that they would not stop for anything except a police roadblock.

The short-run loser, said Macaula, is the Cradock community, which has lost its most important leader. But in the long run, some analysts believe, the loss may prove to be white South Africa's, as a black leader with a genuine following vanishes from the scene, leaving even fewer figures for whites to negotiate the political future with.

Political scientist Hermann Giliomee of the University of Cape Town said in a recent address, "For the South African government, the only thing worse than having to deal with a strong black leadership in this country is to have no black leadership at all."