When Judge Anton Monstert plumped down his teacup, bolted out of the prime minister's office and gave the press evidence of what is regarded here as South Africa's worst political crisis, his action was hailed as proof of the independence of South Africa's judiciary and the freedom of its press.

The euphoria, however, was a bit premature.

An embarrassed and shaken government, in an attempt to contain further disclosures and limit repercussions of the scandal, dealt a strong blow to the judiciary by taking Mostert off the investigation. It also has so taken newspapers to task that many fear the press is "entering the twilight of its freedom" as one editor put it.

These initial government reactions to the scandal appear to indicate that in a crisis South Africa's judiciary and press independence rest more on the shifting sands of executive tolerance than on their own solid foundation.

The duel between executive power on one hand and freedom of the press and judicial autonomy on the other is not yet over. Its outcome no doubt depends on how much more emerges in the multilayered scandal that centers on secret government funding for a proapartheid newspaper, The Citizen.

Mostert stumbled onto the Citizen project, which was just one of the varied money deals of the now disbanded Information Department, during his one-man investigation into currency exchange control violations. When Prime Minister Pieter W. Botha's tact with Mostert over a cup of tea failed to deter the judge from releasing evidence of the scandal, Botha dissolved the one-man commission.

Mostert was replaced by a hand-picked three man judicial commission of inquiry, headed by Supreme Court Judge Rudolph Erasmus.

The Erasmus commission operates under the protective shawl of "subjudice," effectively preventing newspapers from printing anything about the scandal.

The termination of Mastert's commission under such circumstances is unheard of in South African legal history and is somewhat akin "to terminating a trial in midstream," said University of Witwatersrand law dean John Dugard. "It will inevitably be seen as interference with the independence of the judiciary."

That is exactly what opposition parties and a sector of the legal community have called it.

"This is the first sign of conflict between the executive and the judiciary," Dugard said. "And it's not so much a fluke as a reflection of the differences in style between Botha and [former prime minister John] Vorster. Vorster was a lawyer. Botha isn't, so he lacks a sensitivity to the independence of the judiciary."

After effectively silencing Mostert, Botha took on the press. In a speech to cheering party supporters a week after the scandal broke, the prime minister accused the press of publishing "one-sided evidence" without hearing the other side of the story. He added that if the law was not strong enough for the press, "Parliament would look into it," thus raising once again the threat of stricter curbs on an already circumscribed press. This threat was repeated a few days later in a closed meeting with newspaper publishers where Botha "did some serious finger-wagging" at the publishers, an informed source said.

Still on the offensive, Botha next announced he was referring to his legal advisers an editorial in the Cape Times that called on Vorster, who is now President, to step down until the scandal is cleared up.

The editorial was "presumptuous," he complained.

The government has played roughest with its fiercest opponent in the press - the English-language Rand Daily Mail - whose editor, Allister Sparks, and reporter, Hamish Fraser, have been charged with contempt of the Erasmus commission. The charge stems from a front-page story detailing how $31 million in public funds went into launching and running the Citizen. Another $23,000 is being lost each month that the deficit-ridden Citizen continues to publish, they reported.

Their contempt trial, however, brought an ironic twist to the government's efforts to contain and play down disclosures of The Citizen's funding The newsmen's lawyer, Sydney Kentridge, called The Citizen's owner to testify about its financing. Johannes Van Zyl Alberts refused to go to the witness stand and the magistrate adjourned the trial until after the Erasmus commission complets its task, giving the newsmen a temporary victory.

Other reporters have been subpoenaed or threatened with subpoenas after writing reports on the possibility of a link between the Information Department scandal and the murder of a top economist and National Party politician, Robert Smit.

All these actions against the press are widely viewed by editors and reporters here as an attempt to intimidate the press, which has aggressively probed the scandal and which has information of other dubious and possibly illegal secret government projects yet to be published, according to several sources.

English-language editors fear the worst.

"I believe we're having our last fling," said one. "We've been tolerated up to now largely because we've been ineffective. But now we've hit on an issue which hits the Afrikaner national government in its heart and soul."

But what is most significant is how the staunchly progoverment Akrikaans-language press has taken the lead in warning the government about its threats to limit press freedom. Willem de Klerk, editor of the National Partys official mouthpiece, Die Transvaler, and the country's most influential political commentator, reacted hotly to Botha's threats.

In an editorial he wrote, "Absurdly many people blamed the press for the whole information furor. But newspapers only told what others did, said and thought. Do they want a Pravda press? . . . For the sake of the Afrikaners, the National Party and Afrikaner principles, the press will continue to differ with whomever necessary and however high."