The South African government, already buffeted by widespread unrest in black areas, now faces the threat of disruptive protests from among its own staunchest white supporters.

President Pieter W. Botha has angered the predominantly Afrikaner civil service by cutting 4 percent off their salaries in an attempt to reduce runaway government spending. There have been angry scenes and cries of "Down with the government!" at protest meetings of traditionally loyal government employes around the country.

Botha announced the salary cuts yesterday, as South Africa slid deeper into its worst recession in half a century, with soaring interest rates, a declining currency, rising black unemployment, a record number of bankruptcies and inflation nearing 20 percent.

With what is expected to be a punishing budget due later this month, Botha included a 3 percent cut in his own salary, those of his Cabinet and members of Parliament.

While businessmen, who have long criticized the wastefulness of a civil service that employs at least half the country's working whites, have generally praised Botha's move, the political repercussions could be serious for his government.

It is already suffering an erosion of support among the Dutch-descended Afrikaners, who are the backbone of Botha's National Party but are having misgivings about the cautious changes he is making to the system of strict racial segregation called apartheid.

Opinion polls show that significant numbers are beginning to turn to a breakaway party of hard-liners, called the Conservative Party. This could turn into a flood as the Conservatives try to cash in on the anger now sweeping the civil servants.

It is a highly charged political issue because the civil service is institutionally identified with Afrikaner nationalism. During the early years of the Afrikaner struggle against British colonialism and the dominance of the economy by the smaller English community, the civil service became a haven for these less well-off whites.

It became a core constituency of the National Party, and after the party attained power in 1948 it expanded the civil service with the establishment of parastatal corporations and turned it into a vast sector of sheltered employment for Afrikaners.

Now cries of "betrayal" and "treachery" are being heard at many of the protest meetings in progress around the country.

The sense of betrayal seems to be greatest among workers in the state-owned railroad service, where many menial jobs like station porters have been reserved for unskilled whites since the Great Depression of the 1930s to protect them against competition from lower paid blacks. Members of the Artisan Staff Association, biggest of the railroad unions, held a meeting in Johannesburg last night at which they roared with anger, stomped their feet and yelled, "Down with the government!"

The association's president, Jimmy Zurich, spoke of the government's "diabolical, immoral deed" in cutting salaries. Though railroad workers are forbidden by law to strike, many at the meeting threatened to do so if the government did not cancel the cuts, which are to take effect April 1. A resolution warning of labor unrest was passed despite shouts that it was "too soft."

South Africa's economic problems stem primarily from a steep fall in the price of gold. The country produces three-quarters of the noncommunist world's gold, and the 44 percent tax revenue from its sale is what has enabled the government to maintain multiple services for the various racial and tribal groups into which apartheid has compartmentalized its 28 million people.

There are separate bus and train services, separate schools, hospitals, ambulances, taxis and even crematoria. Since the establishment last year of new parliamentary chambers for the mixed-race and Asian minorities with their own ethnic autonomy, there are now 18 departments handling education for the various provincial, racial and tribal groupings.

When the gold price touched a record $820 a fine ounce five years ago, South Africa enjoyed the greatest boom in its history and the Botha government was in a position of absolute security. Since then the gold price has fallen steadily, due mainly to the strengthening of the dollar. The closing price on the London market today was $285.25. A rule of thumb used by financiers here is that for every $10 the gold price goes down, the government loses $200 million averaged over a year, indicating an annual loss of more than $10 billion compared with 1980.

With its reduced revenue, South Africa is facing increased costs. The soaring dollar and South Africa's own depressed economy have caused the local currency, the rand, to be devalued by more than 60 percent in a little over two years. This has sent the price of imports rocketing, and last month forced a 40 percent increase in the price of gasoline. Public transport costs have risen an average of 30 percent as a result.

To supplement its depleted tax revenues, the government has increased a general sales tax from 6 to 10 percent and is expected to raise it another 2 to 5 percent in the upcoming budget.

Yesterday the government announced postal and telephone rate increases of 10 to 28 percent. The combined effect is sending prices rocketing, and a food price survey published today showed that basic commodities like bread and rice had increased more than 21 percent in a year.

Social analysts are attributing the unrest that has been sweeping through black areas over the past six months at least partly to the economic hardship being felt in the ghettoes, where unemployment has reached record levels -- up to 40 percent in some areas -- because of the recession.