A judge on South Africa's Supreme Court cleared former information minister Cornelius Mulder today of charges that he obstructed an inquiry into irregularities in his ministry.

The abrupt end to his trial was a victory for Mulder but forclosed the prospect of his using the proceedings to tell "the whole truth" about the political scandal that forced his resignation last year.

Some government officials feared that Mulder, to clear his name, would make new allegations about high level involvement in alleged covert financing of bids by American publisher John McGoff to buy The Washington Star and The Sacramento Union.

It is suspected widely that Prime Minister Pieter W. Botha knew the details of these two alleged projects, for which $11.5 million was taken out of his Defense Ministry's funds.

The government still faces the threat of more damaging disclosures at the forthcoming trial of Mulder's top aide, Eschel Rhoodie, who ran the secret projects. He has been charged with seven counts of fraud or theft. Today's ruling in Mulder's case is not expected to affect Rhoodie's trial, which is to start Sept. 24.

The charge against Mulder stemmed from his refusal to testify a second time before a government-appointed three-man team probing the multimillion-dollar scandal that involved covert projects to improve South Africa's image abroad.

Supreme Court Judge J. C. Boshoff ruled in Pretoria that Mulder was justified in refusing to testify a second time before the commission because the topics that the investigators wished to probe -- that is, the alleged bids for the American newspapers -- were not legally within the commission's mandate.

Boshoff said the commission had been ordered only to inquire into "new facets and areas revealed in its first report" of last December. Since the newspaper projects were revealed to the commissioners by new testimony in January, they were not legally within the purview of the probers, Boshoff said.

The final report of the government investigators issued in May found Mulder and Rhoodie principally responsible for what was described as a secret deal with McGoff to buy the two newspapers. The probers said that of $11.5 million allegedly provided to McGoff for these purchases, $6.3 million was unaccounted for.

The probers recommended that the government seek legal advice into the possible liability of Mulder and Rhoodie for this loss.

While the ruling today calls into question the legal standing of some of the probers' findings, it is unlikely to lead to a review of their conclusions. It also is unlikely to have any political repercussion. Although Mulder would like to return to public life, most observers say they see no future for him in the political arena here.