An appeals court today overturned the fraud conviction and six-year jail sentence of former South African information secretary Eschel Rhoodie on charges connected with a multi-million-dollar clandestine propaganda effort that led to this country's worst political scandal.

Rhoodie, the mastermind of the covert campaign to influence Western decision-makers and public opinion, was the only person criminally charged as a result of the scandal. Disclosure of the secret campaign forced a prime minister, a powerful Cabinet minister and the country's intelligence chief to resign in disgrace.

Governmental investigators found that nearly $72 million had been illegally diverted over several years for the secret campaign. But the government has failed to show any obvious improvement in its relations with the rest of the world as a result of the effort.

There was little immediate reaction to Rhoodie's successful appeal from either the government or the public. Both have lost a great deal of interest in the scandal, which came to be known as "Muldergate" after Cornelius Mulder, the former minister of information for whom Rhoodie worked.

Rhoodie, 47, the son of a prison guard was both ecstatic and characteristically combative after the decision.

"I feel like someone who has come over the Berlin Wall," he told reporters in Pretoria today. He promised that when his book and one by his wife, Katie, were published, "heads would roll." The implication was that he would release information that could embarrass the government.

Some observer doubt, however, that the flamboyant former civil servant knows or would reveal much more than is already public knowledge.

Under the covert program run by Rhoodie with the knowledge of Mulder, former prime minister John Vorster and former spy chief Henry Van Den Bergh, all of whom resigned from office, the state secretly funneled more than $32 million into an English-language newspaper that pushed the cause of the Afrikaner-dominated government and its policy of racial segregation, or apartheid.

The clandestine activities of the government included more than 100 projects, most of which have remained secret. Among those revealed was an unsuccessful attempt to buy the Washington Star through Michigan publisher John McGoff in 1974. Other projects involved the secret purchase of shares in an overseas television news company and publishing companines.

There were reports also of bribery of Western and African government officials and payment to the campaign coffers of former president Gerald Ford and President Carter. None of those reports, however, have been verified.

The most important result of the scandal was the resignation of Vorster, who was replaced by Pieter Botha in September 1978. Political pressures on the new Botha administration to assign blame for the most flagrant misappropriations of state money centered on Rhoodie.

Protesting his innocence, Rhoodie fled South Africa and settled in France. After charging him with fraud and theft, the government extradited him from France in August 1979.

He was found guilty Oct. 8 of misappropriating $76,000 of the secret $24 million slush fund he controlled and using it for personal real estate deals, including the purchase of a seaside apartment.

Judge Charl Theren disbelieved Rhoodie's defense that the money put into his own account was actually reimbursement for payments he had made out of his own pocket to "anonymous collaborators" working in "highly sensitive operations" for the South African government. At one point Theren said he found Rhoodie's testimony a "made-up story."

In its judgment today, however, the appeals court said that discrepancies in Rhoodie's testimony were not of crucial importance and that in light of the evidence, his explanations were, at least, possibly true. The state, therefore, had not proved him guilty of larceny and fraud, the court ruled.

Instructions to Rhoodie to conduct a "psychological and propaganda war" meant that he had to act unconventionally and take exceptional risks, the court ruled. Against this background, Rhoodie's explanation, which might otherwise be suspicious, were acceptable, the court said. Because of the nature of his duties he could not have been expected to handle financial matters in the normal way expected of civil servants, the judgment said.

The government says it still runs more than 60 of the 100 secret projects that were being conducted at the time of the "Muldergate" scandal. There is speculation some of them involve secret arms purchases.

One of Rhoodie's former top aides last week told a luncheon meeting of American businessmen in Johannesburg that there has been " a lot left untold" about the activities of the former information department. Les De Villiers, who now lives in New York where he works in public relations, also told the Americans that South Africa still needs secret activities because of its political isolation.