JOHANNESBURG, DEC. 23 -- A U.S. measure that calls for double taxation of the 168 American companies still operating in South Africa has heightened fears among some here of an imminent wave of disinvestment.

The repeal of tax credits that American firms receive in the United States for taxes they pay to the South African government is expected to add $43 million to the companies' tax bills over two years -- $20 million in the first year -- and increase pressure on marginally profitable firms either to shut down or sell their operations to South African interests at bargain prices. The repeal was part of this week's U.S. budget legislation.

"Naturally, it will have a severe impact on the profitability of U.S. companies," said Ian Leach, president of the American Chamber of Commerce here. He estimated that the measure will increase the firms' total tax burden to 72 percent from 57.5 percent.

Adrian Botha, the chamber's executive director, said the law will "lead to a deluge of disinvestment."

South Africa's foreign minister, Roelof F. (Pik) Botha, charged tonight that repeal of the tax credits amounts to a "deliberate effort to destabilize South Africa economically" and will sacrifice the jobs of thousands of blacks.

In a harshly worded statement issued in Pretoria, minister Botha said such steps to encourage disinvestment reflected an "ineffectual, immoral and bankrupt policy" that solves none of South Africa's problems.

"The decision is a particularly gross form of hypocrisy. Under the pretense of contributing to peaceful change, it in fact encourages polarization and conflict," Botha said. "Counterproductive and irresponsible as this legislation is, South African interests will doubtless seize every opportunity to benefit from it by acquiring valuable assets on advantageous terms."

{In Washington, the State Department accused Congress of threatening the livelihood of U.S. firms operating in South Africa by adopting the measure to deny them tax credits, the Reuter news service reported.

{"The ultimate intent of this provision is absolutely clear. It is an attempt to use the U.S. tax code to drive American businesses out of South Africa," State Department spokeswoman Phyllis Oakley told a news briefing.}

Some analysts said the corporations hardest hit by the new law would be big oil firms, such as Mobil Corp., that maintain refineries and hundreds of retail outlets here and already pay high taxes. Said Robert Angel, chief executive of Mobil's South African affiliate, "The ramifications seem to be that it will greatly increase the cost of doing business here."

The president of the Association of Chambers of Commerce, Alec Rogoff, said the measure was motivated more by U.S. domestic politics than events in South Africa. "It is counterproductive. It will not create jobs, it will destroy them," Rogoff said. "Some companies will no doubt be forced by this measure to disinvest, but hopefully others will find ways to enable them to stay on in South Africa."

But some trade analysts said that most of the U.S. companies that are likely to divest -- either for moral or economic reasons -- have already done so, and that major firms such as Mobil, with assets of nearly $500 million and more than 3,300 employes here, would absorb the tax bite and remain.

The tax-credit repeal was contained in an amendment to the Omnibus Budget Reconciliation Act passed by Congress earlier this week and designed to trim $76 billion off the U.S. budget deficit over two years.

Drafted by Rep. Charles Rangel (D-N.Y.) to increase pressure on the South African government to dismantle apartheid, the clause was mostly lost in debate over aid to Contra rebels in Nicaragua, welfare spending and farm subsidies.

But it was described in an editorial this week in the influential South African financial newspaper, Business Day, as "one of the most savage sanctions moves which could be imposed on this country."

The newspaper said the measure "could well be the last straw for those U.S. companies which have not yet quit."

Some economists, however, said the U.S. tax change is not likely to trigger a stampede of disinvestment.

"Some obviously will have to withdraw, but the larger number will remain. They're making immense profit in South Africa, and this isn't enough to push them over the edge," said Carl Noffke, director of the Institute of American Studies at Rand Afrikaans University.

"The companies that wanted to get out have already left," he said. "The rest have already lived through the worst. Now there are indications that they can look forward to increased profits in the years ahead."

In the past two years, 96 American corporations -- many of them making little or no profit -- have pulled out of South Africa. Of these, 45 sold out to local interests but retained licensing, royalty and technology transfer agreements, which allow them to continue profiting from the sale of their products or services here, according to the Investor Responsibility Research Center, a Washington group.

In the past five years, 143 American firms have withdrawn from South Africa, according to the American Chamber of Commerce here. Fourteen others have announced they intend to sever ties to South Africa but haven't done so.

Of the firms that remain here, the largest are Mobil Corp., with 3,342 employes; RJR Nabisco Inc., with 2,479 employes; Goodyear Tire & Rubber Co., with 2,471 employes; USG Corp., with 2,239 employes; Caltex Petroleum Corp., with 2,140 employes, and Johnson & Johnson, with 1,376 employes.

U.S. firms still operating here raised virtually no public opposition as the tax credit repeal made its way through Congress.

Noffke and other trade analysts speculated that the American companies wanted to avoid drawing attention to their South African interests.

CAPTION: Roelof F. Botha.