South African police and troops raided another major black township today as racial unrest continued to disrupt these segregated living areas.

A force of undisclosed size moved into the township of Tembisa, about 20 miles east of Johannesburg, which has been the scene of almost continuous disturbances for the past six weeks.

A police spokesman, Col. Leon Mellet, said the operation would continue "for several days" and was aimed at rooting out a criminal element that was aggravating the unrest.

Mellet did not disclose the results of the raid -- the third in black townships near Johannesburg in the past three weeks -- but said 50 blacks had been arrested in Tembisa during the past week.

Meanwhile, rioting youths set fire to buildings and vehicles in Atteridgeville township, near Pretoria, today after the funeral of a 13-year-old black boy who was killed by a police rubber bullet during disorders there last week.

Hundreds of mourners carried the coffin of Wallace Ramkin through the streets of Atteridgeville to the cemetery, then went on the rampage, police said.

The current wave of unrest, which Law Minister Louis Le Grange said last week had become more serious than the 1976 disturbances, began in August as the white-minority government introduced a new constitution that amended the segregationist system called apartheid by giving a form of parliamentary representation to the mixed-race and Asian minorities but not to the black majority.

After repeated clashes with the police and with the casualty rate rising above 50 killed and 500 injured, the police and Army encircled three townships south of Johannesburg with a force of 7,000 before dawn on Oct. 3 and conducted house-to-house searches of all of the estimated 225,000 inhabitants.

Le Grange said at the time that the raid was to eliminate "revolutionary elements" behind the unrest, but none of the 358 people arrested was charged under the security laws. Most were released after paying nominal fines for minor violations.

Eight days later, these townships of Sebokeng, Sharpeville and Boipatong, and a fourth, Bophelong, were raided again.

Yesterday, police returned and detained several members of the Vaal Ministers Solidarity Committee, which has become the focal point of local resistance to apartheid. Among those detained was Lord McCamel, the chairman of the interdenominational committee.

At the same time the security police detained another official of the country's biggest labor organization, the Federation of South African Trade Unions, which joined a call for a two-day strike last week in protest against the government's handling of the disturbances.

The official, Bangalizwe Solo, was the fourth labor union official to be detained since Friday, including the federation's president, Chris Dlamini.

These detentions, under a law that allows the prisoners to be held indefinitely in solitary confinement without trial, have prompted warnings by unionists of an industrial confrontation.