In an unexpectedly forthright report, an Afrikaner judge has blamed aspects of South Africa's apartheid system and insensitive attitudes on the part of some government officials for the June 1976 outbreak of violence in Soweto, which triggered 18 months of nationwide turmoil and rioting that left 575 dead.

Black leader and government critics have welcomed the report released March 1 by Judge Piet Cillie for its frankness and for countering the claim of many government officials at the time that the upheavel, which caused $55 worth of damage to government buildings, was the product of a conspiracy by communist agitators.

At the same time, however, they warned that the key policies existing in 1976 are still in force.

"It is an extremely serious matter that the same factors that existed four years ago are still there and form the foundation of government policy," said Frederick Van Zyl Slabbert, leader of the official opposition party.

Several black leaders warn that similar violence could happen again. "While we indulge in semantics, the clouds -- very dark clouds -- are gathering around us, black editor Percy Qoboza wrote. "Just the same as I warned they were just before that fateful morning of June 16, 1976.

Cillie's conclusions, reached after a 3 1/2-year investigation during which he heard testimony from 563 people may bolster Prime Minister Pieter W. Botha's campaign to get whites to accept the need for change. It carries added weight because it comes from a respected member of the Afrikaner minority government.

According to Cillie, those policies that contributed to a mood of frustration and set conditions for the unrest included aspects of segregated schooling, the system of separate homelands for blacks, salary discrimination, dentention without trial, laws that segregate residential areas and that restrict blacks' movements and job opportunities, the denial of South African citizenship to blacks, the denial of the right to own property in urban areas and the lack of any say in official government bodies.

"Nearly all legislation relating to relations between the races is divisive by nature and is regarded by the black man and the colored [mixed race people] as injustice and discriminatory. Discrimination, which is always considered unjust, did not only cause dissatisfaction, but among many, a great hate. This dissatisfaction and hate was one of the foremost creators of a spirit of unrest," Cillie wrote.

As for the initial outbreak of violence of June 16, 1976, a day that shocked this racially divided country and drew international attention to the black township of Soweto, the jurist said it stemmed from the insistence by the Education Department that the Afrikaans language had to be used for at least 50 percent of the teaching time in the black secondary schools.

Although organized protests by black students precipitated the confrontation with police, insensitive and ill-informed education officials and an unprepared police force had to share in responsibility for the day's events, Cillie said.

Education officials failed both to assess the explosive situation or to take measures to defuse it. "First, avenues of communication were closed," Cillie wrote. "There was no opportunity to discuss policy and to explain reasons for the policy; there was no exchange of ideas and the impression was created that the authorities were inaccessible and forbidding."

Cillie faulted the police for not knowing the student demonstration was coming, although plans were afoot for three days beforehand. He concludes that on that fatal day police only fired on the students after policemen had been stoned and felt they were in danger.

But the judge noted that in some cases in the following months individual policemen acted too hastily and harshly and at times "fired too quickly." Although 451 of the deaths during the turmoil were caused by police, no officer has ever been charged with one.

All Cabinet ministers were absolved of responsibility for the rioting because middle-level officials kept them badly informed, Cillie said.

Two of the most significant aspects of Cillie's report are his exoneration of the press from any responsibility for causing or prolonging the unrest and the absence of any accusations of incitement against more than 50 black leaders who were detained in October 1977, while 18 of their political organizations were banned.

Most of the banned organizations were affiliated with the black consciousness movement of which Cillie says: "a philosophy, almost a religion, its purpose was to make blacks proud and conscious of their being black and to create greater solidarity among blacks. It led to polarization between black and white and created a useful climate for agitators."

Of the "Black Peoples' convention" to make black youths conscious of unrest, Cillie said: "Its greatest contribution towards unrest was its attempt to make black youths conscious of their position as blacks through the philosophy of black consciousness."