At least 35 persons were wounded when police opened fire on black youths during disturbances in two South African cities today, the fourth anniversary of the Soweto race riots.

Earlier this morning, a white policeman was stabbed to death during a clash in Cape Town, officials said.

Police said they opened fire with shotguns on a crowd of black youths near Soweto when they discovered the youths looting a shop. Twenty persons, including several children, were injured non seriously according to a hospital spokesman.

In the city of Bloemfontein, 220 miles southwest of here, 15 black youths were wounded slightly when police fired buckshot at them. Police said the youths were stoning cars and buses and that they refused to disperse when ordered.

As the outbreaks of violence continued, police charged that foreign journalists were "openly inciting" black youths to "stone-throwing and riotous behavior." Reporters were banned today from "trouble spots" in South Africa, including black townships in most urban areas. Only selected journalists will be allowed in, and they will be under escort.

The ban follows police aggression toward reporters and photographers yesterday and today in Soweto, in which officers lobbed tear gas canisters directly at journalists and, according to some, threatened them.

In announcing the ban, Police Commissioner Gen. Michael Geldenhuys said that some members of the South African press had informed police that they saw incidents where "certain pressmen, especially those attached to foreign news media and television networks," were inciting black youths.

A similar police ban was imposed on the news media in 1976, when approximately 600 people died in race rioting that began when black students struck to protest the government's policies, of apartheid, or racial separation.

Four years later, there has been no hope revived in the sprawling black township just west of here, and no reconciliation between blacks and whites or their government.

Most of Soweto's leaders not exiled, jailed -- or dead -- are banned from political activity. Those who remain, like Bishop Desmond Tutu and physician Nthato Motlana, were told yesterday that even commemorative services for those who died in what blacks call the "rebellion of 1976" came under a ban imposed Friday on all meetings in the country for the rest of the month.

The black leaders say the government action is comparable to a ban on services during the "Day of the Covenant," the day most revered by Afrikaners -- whites of Dutch descent who dominate the government. Each year on that day, they commemorate the victory of a few hundred afrikaner pioneers over thousands of Zulu warriors.

At one point yesterday, blacks who showed up for a commemorative service gathered to kneel together in a field outside the locked church in Soweto where the meeting was to have been. Others joined a group that traded insults for four hours with police, who eventually dispersed them with tear gas.

The head of Soweto's security police, Maj. Schalk Visser, also showed up at the gathering. Asked the reason for the ban on all meetings, Visser said, "What is the purpose of a commemorative service? To sort of activate people, isn't it? Soweto has been quiet for the past week, for the past month. We didn't have any incidents at all. Why should we have incidents now?"

Visser's remarks gave the rationale for the ban. Without meetings, the people would not be "activated." Soweto would be calm.

But four years after the riots, Soweto remains a community with a formidable police presence. Detentions are commonplace among political activists. Gatherings and Social occasions normally are monitored by hundreds of police informers. Roadblocks go up periodically as police search for smuggled arms and suspicious persons.

Whites, coloreds (mixed race) and Indians require permits to enter the township. The police department plans to spend $3 million on a new complex to house riot police there. Police stations are surrounded by tall fences and studded with floodlights to deter guerilla attacks.

Unable to organize, the Soweto leadership that refuses to cooperate with apartheid structures has become ineffective. Letgay Mathabathe, a member of Soweto's "Committee of Ten," arrived Sunday at the church three hours after the meeting was to begin and well into the seesaw confrontation between the police and the youths.

The committee had not made any complaints to the government about the ban on meetings. "We didn't think it would be useful. We knew they wouldn't listen to us. It doesn't help, it doesn't help, it doesn't yield anything at all to talk to the government," Mathabathe said.

"There is no relationship between the people and the authorities in Soweto," he said eyeing the police on the opposite corner. "They are poles apart. The only thing it will lead to is we will go at each other's throats." a

Mathabathe, a former schoolteacher who resigned in 1976 to protest blacks' inferior school system, was detained by the police in 1977 for five months. Now holding a top job in a large South African firm, he is not a radical. But he is too obstreperous for the government and too moderate for the youth.

For the future, black editor Percy Qoboza today offered what he called a "certain" prediction in his newspaper, the Johannesburg Post. "The day when this nation celebrates June 16 as an offical commemoration day is inevitable. I'll make one other prediction," he wrote. "It will happen in the life span of the present generation."

In a telling exchange at the church yesterday, Police Brig. D. J. Crafford sharply ordered black youths to go home.

"I am giving you five minutes to disperse," he said. "There is no meeting.

It's been prohibited by the government."

Directly in front of him a black teen-ager responded sullenly: "It's our country, not the government's country."

At one point, the youths knelt down and sang what blacks call their "national anthem." But they did not remain kneeling long. And when they were back on their feet, they sang a different song -- "Sizobadubul Nqo Mbayimbayi" -- Zulu for "We Shall Shoot Them With Guns."