The United States cautioned South Africa yesterday that its attempts "to stifle the freedom of expression" for black organizations and journalists can damage relations between the two nations.

In its strongest, specific criticism of the Pretoria government's actions, the Carter administration deplored them as "a very serious step backwards" from the policies which it has urged upon South Africa.

"Our relations will hardly be improved by what has happened," the State Department said. Once the United States has more details "about the bannings and arrests," the department said, "we shall examine very closely the implications of these events with regard to U.S. South African relations."

South Africa's ban on numerous black organizations arrests of black leaders, and the shutdown of the largest black newspaper put the Carter administration; in a position in which repeated American admonitions about its racial apartheid policy appear hollow.

A delegation of U.S. Congressmen who met with State Department officials yesterday said the Carter administration initially should at least recall the American ambassador to South Africa, to demonstrate disapproval of that nation's racial actions.

Rep. Andrew Maguire (D-N.J.) said he and four other congressmen in the delegation want some specific action to "disentangle the United States" from economic and other relations with South Africa. He mentioned, as a starter, legislation to suspend Export Import Bank loan guarantees for American business investments in that nation.

"This is a watershed in terms of internal developments in South Africa," Maguire said, "and it ought to be a watershed in U.S. South African relations."

Others attending the meeting with William B. Edmonson, deputy assistant secretary for Africa, were Edward J. Markey (D-Mass), Thomas J. Downey (D-N.Y.), Charles C. Diggs Jr. (D-Mich.) and Paul E. Tsongas (D-Mass.).

Sen. Dick Clark (D-Iowa) said the South African government is "deliberately deepening divisions that will only lead to racial confrontation" and with that pattern, "relations between South Africa and the United States will inevitably worsen. . ."

The administration's sharp criticism of South Africa, however, raised other questions, namely, whether the Carter administration is inconsistent in its human rights campaign.

State Department spokesman Hodding Carter III was asked at a news briefing to explain why the administration was so critical of human rights policy in South Africa, while it appeared to be muting its criticism of human rights in the Soviet Union.

Carter denied that the administration is softening its advocacy of human rights in the Soviet Union, although there the administration has shifted from public assusations to private diplomacy. "The approach that is taken in each instance," Carter said, "can go down a number of avenues."

On Tuesday, Carter noted, in Washington and at the Belgrade conference on East-West detente and human rights, the Carter administration strongly criticized prison sentences meted out to four of Czechoslovakia's prominent human rights activists.

Arthur Goldberg, he chief U.S. deliegate to that conference, has been reported to be at odds with order delegation members over the intensity of his championship of human rights. Carter, however, said Secretary of State Cyrus R. Vance sent Goldberg a message commending him for a stand "that accurately reflects the position of this government."

The question of putting U.S. pressure on South Africa is a complex matter for the Carter administration. The United States simultaneously is seeking South Africa cooperation in bringing independence and majority rule elsewhere in southern Africa. South Africa rules Namibia (Southwest Africa), and its controls the economic lifeline of Rhodesia, both governed by white minorities.

South Africa "has been constructive" on the Namibian and Rhodesian issues, the State Department's Carter said.

In addition, as he acknowledged yesterday, South Africa's press is much freer than in most Afircan countries, black or white. "There's no question," Carter said, "that the operation of a free press in South Afirca has been one of the chief and valid claims by that country to having an open society, at least in that respect."

However, Carter said, that is also what makes the new "curbing" of the press in South Africa a cause for unusual American concern.

In a formal statement, coodinated with the White House, the State Department said the United States is "deeply disturbed" by South Africa's decision "to ban over a score of organizations and publications and to detain or ban persons associated with the promotion of the rights and welfare of South Africa blacks."

The statement continued: "The banning of South Africa's largest black newspaper. The World, and the reported arrest of Percy Zoboza. The World's courageous editor, and other black leaders," will be regarded by the international community as steps "to stifle the freedom of expression by spokesmen for black aspirations in South Africa."

Also criticized were the banning of other organizations, black and interracial, "as well as the banning of a number of prominent whites. . ."

The United States has "set no timetable" and "offered no blurprint" for "clear movement away from apartheid and the regressive laws that undergird" it in South Africa, the statement said. But, it said, "we firmly believe there must be the beginning of a process in which all the people of South Africa can engage in a dialogue leading to decisions about their economic, social and political future."