For the first time since 1976, a major American bank has agreed to participate in a publicized loan to the South African government.

In a reversal of stated practice, Citibank -- owned by Citicorp, the nation's largest financial holding copany -- has joined three other international banks in negotiating a $250 million syndicated credit to finance schools and housing for South Africa's black population. A Citicorp spokesman said agreement on terms is expected this week at which time the loan managers will seek to interest other banks in providing portions of the funds.

The loan represents a success for South Africa's policy of vigorously courting the confidence of the international financial community as one means of strengthening the hand of Prime Minister Pieter W. Botha.

"The confidence factor is very important," Simon Brand, Botha's chief economic adviser, said in an interview with Africa News in Pretoria earlier this year. "Lots of political plans depend on the economic base, and it is not alwasy easy to marry political objectives with economic realities."

The attempt to convince American business that its economic support encourages political reform is to continue Thursday at a scheduled meeting between South Africa's Finance Minister Owen Horwood and about 80 bankers in New York City. Horwood, who will be en route to Washington to attend the annual meeting of the International Monetary Fund and the World Bank, also is planning to meet U.S. business executives in Houston and Chicago.

Citicorp's decision to participate in a direct loan to the government is a sign that the financial community already perceives an improvement in South Africa's image internationally. In 1978, after domestic turmoil in South Africa prompted renewed public scrutiny of corporations with interests there, several American and European banks announced restrictions on their lending practices.

Citicorp, in a statement to shareholders at the time, called apartheid "a negative effect on South Africa's economic viability."

"So long as this is the case, we will continue to moderate our business involvement in the country," the document declared. "Specifically, Citicorp is not making loans to the government of South Africa."

A Citicorp spokesman denied that the new quarter-million-dollar loan represents a substantive shift but pointed to a bank statement in January which signaled a new readiness to review government loan applications by announcing that "Citibank is now prepared to consider selctively loans to both the private and public sectors in South Africa."

"We said we would participate in loans that we determine would have a beneficial effect for all South Africans," said the spokesman. "This fits that category."

The participating banks, led by Dresdner of West Germany and including Barclays of Britain and Union Bank of Switzerland, have insisted on a "needs and purposes clause" in the loan agreement to restrict the money for educational and housing needs. And this, they expect, will dampen criticism of the deal.

But critics already are mobilizing protests. The National Council of Churches, a leader in the campaign to alter or end U.S. business ties with South Africa, has appealed to 11 other major banks to refrain from involvement. "I expect there will be a chorus of opposition to this loan from churches, universities, unions, the black community and congressional leaders and many institutional investors," said council President William Howard.

George Houser, executive director of the American Committee on Africa, a New York group that has coordinated previous antilon campaigns, charged that Citibank is quick to step in whenever South Africa gets into trouble.

"In 1960 after the Sharpeville massacre alarmed the foreign economic community," Houser said, "and in 1976 after the Soweto uprising again raised concern, Citibank provided financing to help restore international confidence."

In spite of the criticisms, South Africa is expected to obtain favorable terms, as it did in several other forays into the money market earlier this year. West German banks have made two loans to government agencies and Citicorp comanaged a $50 million deal for a private South African bank.

Financially, South Africa has far less need of the money than in 1976 and 1977, when unrest sparked a record outflow of capital and loans were required to fill the gaps. Most of those have been repaid. Gold prices and production are up, and the country is considered "under borrowed."

"What is important to South Africa at this time," said one American banker who asked not to be identified, "is the optimism this loan represents toward Botha's policies and his effort to end South Africa's isolation."

During the next decade, the country plans to spend nearly $30 billion on capital improvements, including black housing and schools but concentrating on strategic and defense-related projects.