A nationwide opinion poll has found that most Americans disapprove of South Africa's racial suppression and believe the United State should support efforts to give blacks equality with the ruling white minority.

But the poll also indicates that Americans, by a significant majority, opposed aiding black groups in South Africa that advocate violence. The majority also believes that, even if the Soviet Union and Cuba intervene militarily in South Africa, the United States should not become involved.

These are the principal findings of the poll done for the Carn egie Endowment for International Peace by a private research organization, Response Analysis Corp.

The results, which are being made public today, are based on telephone interviews with 1,000 persons in different parts of the country. Officials of the Carneige endowment, a private, nonprofit foundation engaged in scholarly research, said they believe the poll is "the most thorough survey ever taken of American attitudes toward South Africa."

In many respects, the results bearstriking similarities to recent polls on U.S. attitudes toward such other global trouble spots as the Middle East and Southeast Asia. These polls have displayed what some analysts refer to as "a post-Vietnam syndrome."

Essentially, they indicate that the majority of Americans want their government to pursue policies promoting world peace, democracy and equality for all people. But this support emphatically does not include any policies or actions that could result in foreign military involvement by the United States.

That is the case with the South Africa survey. It finds that, despite South Africa's heavy investment in trying to create a favorable image here, Americans, by majorities of up to 86 percent, condemn South Africa's racial segregation laws and its use of force to keep blacks subservient.

By similarly big majorities, the poll finds Americans support public statements by the U.S. government condemning South Africa's racial policies and favoring U.S. support for black groups there that advocate peaceful change.

But, by a ratio of 77 percent to 11 percent, the poll shows a respondents opposing U.S. support for South African blacks seeking to change the system by use of violence.

In response to questions about whether the United States should intervene if the level of South African violence increases or if the Soviets and Cubans step in, the overwhelming majority said the United States should not become involved.

The poll does indicate support among Americans - although by much narrower margins - for more limited steps such as joining a United nations call for trade sanctions against South Africa and generally limiting trade with countries that "do things that go against our sense of right and wrong."

On the general question of whether the United States should stay out of the internal business of other countries, responses were almost equally divided. The poll showed 43 percent favoring such a course, and 42 percent disapproving of it.

The poll also found that American blacks have the greatest interest in South Africa and are the most emphatic in calling for pressuring South Africa to change racial policies. Yet, American blacks - like whites - also reject U.S. military involvement.