The South Africa government, under increasing international pressure and press scrutiny because of its radical policies, is gradually imposing a form of cesorship designed to curtail reporting on three sensitive issues.

New legilsation promulgated during the past three months restricts press inquiries into police activities, deaths from unnatural causes and South Africa's source of oil supplies.

South Africa editors so far have been powerless to stop the legislation, which applies to both local and foreign correspondents.

In fact, the government traumatized recently by the country's worst political scandal, showed it was prepared to go to even greater lengths to protect itself from damaging news reports when recently it proposed a law prohibiting the press from reporting allegations of government corruption.

Although Prime Minister Pieter W. Botha withdrew the controversial "cover-up" proposal, the lesson lingers with South African journalists that they would have been impotent to stop passage of the measure through the legislature, dominated by the ruling National Party. Since South Africa has no high court review of parliamentary acts, the press also had no judicial recourse against the proposed law.

On top of the new legal restraints, South African journalists, especially black ones, face the added risks of continued and steady police surveillance, which can land them in court or jail if they are working on a controversial topic.

Zwelakhe Sisulu, 28, black news editor of the Johannesburg Sunday Post, was sentenced this week to nine months in jail for refusing to answer questions about telephone conversations he had with one of his reporters. The reporter, Thamsanqa Gerald Mkhwanazi is being held incommunicado by security police. The police are seeking information about an alleged offense under the country's security legislation.

The case has the added ingredient of being one of rare times that police have admitted they tapped a journalist's phone because they claim to have proof the telephone conversations took place, Sisulu said. Most journalists here routinely assume that their phone conversations are being monitored.

Sisulu also is president of the Black Journalists' Association and his father is serving a life sentence at the political prison of Robben Island. He is out on bail while he appeals the sentence, which was given in closed session.

A white journalists, John Matisonn, faces 14 days in jail for a similar refusal to answer questions in court about his source on a story linking a religious organiaztion to the recent Department of Information scandal. He also is appealing.

The new legislative restriction with the most far-reaching political consequences is one making it a criminal offense to print any "untrue matter" about the police without "reasonable grounds" for believing it to be true. Violators are liable to a maximum fine of $11,800 or five years in prison or both. A similar provision relating to South African prisons has prevented effectively any uncomplimentary stories about jail conditions in the last 10 years.

In a country where oppostition to the government's apartheid policy is held in check by a strong police force, which is allowed to hold persons incommunicado for indefinite periods, some journalists view this measure as much more serious than the much publicized one that sought to stifle corruption reports.

"The central issue in this country is not corruption, it's still race relations," said one white journalist.

Under the new law, the onus of proof that the reporter had "reasonable grounds" for printing his story rests with him, which means he would be required to reveal his sources to prove his information is correct.

As the main opposition daily, the Rand Daily Mail, commented: "In effect, the law means the press would be barred from publishing a report about the police should the police refuse to verify it. So, in practice, only the police version of any event would be made public."

Should there be future upheavals like those that wracked urban black communities in 1976 and 1977, or mass protests against apartheid, the new laws are likely to make press reporting of these events more difficult since they normally entail police activity. Foreign journalists usually are prohibited from entering black townships when there is unrest there.

A second major area cut off from press inquiry concerns deaths from unnatural causes. So, for example, press probes into deaths that occur in police custody - such as the investigations of news media into the death of black consciousness leader Steve Biko - will be checked.

Press reporting on such deaths is prohibited under the new legislation in order not to "prejudice or anticipate" the findings of official inquests.

Both these new restrictions are widely seen as attempts to prevent more negative publicity for the South African police force, whose image has been badly tarnished by press reports of its actions during the riots and later, during the inquest into Biko's death revealing the mistreatment he suffered while in police custody.

A third law passed during the last legislative session clamps down on the publication of stories about South Africa's Achilles heel - its oil.

The country's oil requirements, reserves and supply sources are out of bounds for newspaper pages.

A similar ban was also imposed on reports about firms that manufacture or stockpile any strategic goods. Penalties include a maximum fine of $7,140 or imprisonment for a period of up to seven years or both.

The new limitations affect foreign coverage of this racially tense country.

According to newspaper lawyer Kelsey Stuart, foreign correspondents living in South Africa are as liable to the press curbs as South Africans are. Although the government has not yet charged any foreign journalist with violating press restrictions, the mere presence of the laws on the books inhibits correspondents who do not want to risk expulsion.