JOHANNESBURG, AUG. 8 -- The manager of a soccer team that once acted as Winnie Mandela's bodyguards was sentenced to death today for the murder of a 14-year-old anti-apartheid activist in December 1988. Witnesses said the killing followed accusations by Winnie Mandela and defendant Jerry Richardson that the victim, Moketsi "Stompie" Seipei, was a police informer.

The outcome of Richardson's lengthy trial now raises the possibility that Mandela, wife of South Africa's most important black leader, Nelson Mandela, may herself be charged with abducting and beating Seipei, who prosecutors said was taken to Winnie Mandela's house before Richardson killed him.

Winnie Mandela's driver and other associates face trial next month on kidnapping and assault charges.

The attorney general for the Witwatersrand region, Klaus von Lieres, said recently that he would assess the evidence against Winnie Mandela and decide whether to prosecute her after the Richardson trial was over.

The issue is a highly sensitive subject for the government of President Frederik W. de Klerk, coming at a time when de Klerk needs to maintain good personal relations with Nelson Mandela if the two men are to negotiate a new constitution for South Africa.

The two leaders reached a breakthrough accord two days ago, when Nelson Mandela cleared the way for the talks to begin by announcing a suspension of the African National Congress's 29-year armed struggle against white-minority rule.

Winnie Mandela became involved in the scandal surrounding Seipei's death, while her husband was still in prison serving a life sentence for revolutionary activities. Winnie Mandela had taken Richardson into her home along with some street youths, apparently to try to rehabilitate them through sports activities and to use them as personal bodyguards in Soweto, the sprawling black township outside Johannesburg where she was the frequent target of harassment by government officials and white extremists.

The youths became known as the Mandela United Football Team, with 42-year-old Richardson as their "coach," although the group never played any football, as soccer is called here. The youths accompanied Mandela wherever she went and became involved in violent feuds with members of black gangs.

According to testimony at Richardson's trial, Winnie Mandela's green minibus pulled up in front of a house on the grounds of the Methodist Church in Soweto's Orlando West neighborhood on the night of Dec. 29, 1988. The house served as a shelter for black youths in trouble and was run by a white pastor, Paul Verryn.

Police testified that four youths, including Seipei, were abducted from the shelter and driven in the minibus to Mandela's house. Three of the youths, Kenneth Kgase, Barend Mono and Gabriel Mekgwe, said Winnie Mandela tried to force Seipei and the others to confess that the pastor was molesting them sexually, which they denied. The three also said Seipei was accused by Winnie Mandela and Richardson of being a police informer.

The youths testified they were whipped and beaten by members of the soccer team to make them confess and that Winnie Mandela participated in the assaults. Seipei, who had led a gang of anti-apartheid activists known as the Under Fourteens, fought back fiercely and suffered severe injuries, according to the witnesses.

Seipei later disappeared, and on Jan. 1 he was found stabbed to death in a Soweto field.

Throughout the trial, Richardson repeatedly denied that Winnie Mandela was present when the youths were beaten. A woman from the small rural town of Brandfort, where Mandela was once banished by the government, testified that Mandela was there and not in Soweto on the day the assaults took place.

The judge dismissed the woman's testimony saying that her evidence "did not impress." In addition, he made a special finding in his judgment that Winnie Mandela was present for at least part of the time during the assaults.

Richardson also was sentenced to a prison term of 18 years on charges of kidnapping and attempted murder of another black youth, Andrew Ikaneng, in January 1989.

But despite his death sentence and the fact that South Africa has one of the world's highest execution rates, Richardson may escape capital punishment because all executions were suspended last February pending the outcome of the government's constitutional negotiations with black leaders.

A recent change in the law also means Richardson will qualify for an immediate appeal to the country's highest court, the Court of Appeals.