A Supreme Court judge has dismissed a lawsuit against the police brought by the widow of a black activist who died in police custody, Washington Post correspondent Caryle Murphy reported yesterday.

Nohle Mohapi disputed the police's claim that her husband, Mapetla Mohapi, committed suicide while in detention.

Mohapi, who was 28 at the time, was arrested July 16, 1976, by security police. Three weeks later, police told his wife that he had hanged himself from a noose made of a pair of jeans strung from his cell window.

The $42,000 suit was being watched closey by legal observers in South Africa because it was one of the rare cases in which the family of a dead political detainee appeared to have concrete evidence to challenge the official version of the death.

Since 1963, when South African security laws suspended the right of habeas corpus, 44 political detainees have died in police custody, more than half of them during the 18 months of violent unrest in 1976 and 1977.

In the case of Mohapi, police said at first that no suicide note was found.

Five months later, they produced a purported note, but the victim's family produced notes Mohapi had smuggled out shortly before he died. These notes were used in court in an attempt to show he had shown no signs of being suicidal and that the handwriting on the police-produced notes was different.

In another development, about 300 black workers at a crucial oil refinery construction site rioted yesterday, setting fire to two vehicles and burning to death one white truck driver, a company spokesman said.

Employes at the SASOL coal-to-oil refinery site south of Johannesburg reportedly were angered by rumors that "military personnel" shot dead a fellow worker over the weekend.