South Africa and its major U.S. and European creditor banks agreed here today to an interim plan calling for repayment of $500 million of its multibillion-dollar foreign debt, bringing a technical end to the payment freeze Pretoria imposed last September.

South African Finance Director Chris Stals, who headed the government team negotiating with representatives of 30 banks, hailed the agreement as "a major step" on "the very long road to normality" for South Africa.

The accord was reached despite last-minute appeals by three leading South African churchmen, including Anglican Bishop Desmond Tutu, that the banks refuse to deal with Pretoria and continue to use financial pressure to help push for the dismantling of the apartheid regime.

Last August, in response to growing antiapartheid activism at home and violent racial clashes in South Africa, major creditors led by Chase Manhattan and other U.S. banks refused to renew maturing short-term loans or to advance South Africa any new money. Pretoria responded by declaring a moratorium on repayment of all maturing loans.

South Africa's total foreign debt is estimated at $24 billion, of which $10 billion is owed to noncommercial sources such as the International Monetary Fund and in government-to-government export credits. Of the $14 billion commercial debt total, most of it short-term, British banks have the largest exposure of about $5.5 billion, with $4.5 billion in the United States and $4 billion in Switzerland, West Germany and France.

Under terms that Stals described as "very advantageous" to the banks, South Africa will make a down payment of 5 percent, or about $500 million, in four phased payments beginning April 1 on the $10 billion in loans maturing by 1987.

In addition, interest rates will be increased by 1 percent on unpaid principal due during the same period. The banks agreed to roll over the unpaid balance for the one-year period.

Next February, South Africa and the banks will meet again to discuss further arrangements to deal with the remainder owed, plus an additional $4 billion in longer-term debt falling due after the March 1987 agreement expiration.

Stals said that South Africa had agreed to the plan "reluctantly" and had argued that the 5 percent down payment was too high. According to figures released this week, South Africa estimates a 3 percent growth rate plus a $2.3 billion balance-of-payments surplus for 1986. Of the surplus, $1.5 billion is destined for payment of debt not covered by the freeze. The extra $500 million, he said, is "an additional burden" that provides little left over.

But the bankers said that the South African economy, after a drastic fall last year, now appeared to be picking up. They insisted on a midterm review of the terms of the agreement this summer to determine if South Africa could pay more.

Following announcement of the deal, antiapartheid activists here charged it was "tantamount to rescheduling of South Africa's debt." But Fritz Leutwiler, the Swiss banker who mediated the accord, insisted that "this is not a rescheduling agreement. The consensus reached" by the banks, he told a news conference, "is of a shorter nature . . . . It is an interim arrangement."

The 30 banks represented at the meeting, including Chase Manhattan and Barclay's, hold 70 percent of South Africa's total $14 billion commercial debt. Late last year, they turned down a South African proposal to extend the payment freeze until 1990. Today's agreement was based on a proposal Leutwiler submitted to the two sides.

Leutwiler said the banks achieved "broad consensus" approving the outline of his plan, with the details to be ironed out by a 10-bank committee over the next several weeks. In addition, Leutwiler said he would inform an additional 230 banks with smaller exposure in South Africa of the accord by telex tonight. He said he expected no significant change in the plan, and all banks would be asked to reply formally to him, rather than South Africa, by early March.

In his separate news conference today, Stals maintained that the agreement "paves the way" for new western bank loans to South Africa. He said his government would "encourage potential South African borrowers to begin working on this immediately."

But Leutwiler said there had been "no discussion of fresh money" in today's talks. He said "the South Africans know there is no question of new money at this time."

Similarly, he said there was no discussion of current political developments in South Africa. He said some banks, especially in the United States, are under "political pressure," but their major concern is that South Africa "continue servicing the debt. They don't want to lose their money."

Stal agreed that politics were not discussed, although "we all understand that in the background there is a political situation."

South Africa last fall engaged Leutwiler as an independent mediator and he said he set today's date for the meeting between the banks and South Africa after South African President Pieter W. Botha's speech last month "convinced him" the government was serious about reforms. "The speech contains clear and concrete undertakings to do away with apartheid," he said.