A private study commission, warning that "time is running out" on prospects for averting major racial violence in South Africa, proposed yesterday several measures it said should be implemented and remain in place until the white minority South African government agrees to "a genuine sharing of political power" with the black majority.

The commission's report, produced after a two-year study financed by the Rockefeller Foundation, proposes several steps by the U.S. government and private corporations that would go beyond the Reagan administration's announced policy of "constructive engagement" with South Africa.

These include an expansion of the U.S. arms embargo against South Africa, use of diplomatic and economic rewards and punishments to influence South African government policy, and encouragement of U.S. corporations with investments in South Africa to play a more active role in moving the country toward a system of shared political power.

Last week, a senior State Department official said the administration's approach to South Africa would be one of "constructive engagement" rather than "confrontation." Instead of negative pressure, he said, the administration approach is to "positively support that which one wishes to see, both by word and deed."

The study commission acknowledged that the United States has "limited leverage" over South Africa and said it is in the U.S. interest to maintain commercial relations with white-ruled South Africa and the nations of black Africa. Many of the commission's findings and recommendations were closer to the attitudes of the Carter administration than the as-yet-unspecified "constructive engagement" policy of the Reagan administration.

The recommendations include expansion of the arms embargo to include foreign subsidiaries of U.S. companies; encouragement of U.S. corporations to stay out of South Africa or, enlarge their operations, and commitment of substantial resources by those corporations toward improving the lives of blacks.

Also included is use of such incentives as federal control over export of high-technology goods to reward or punish the country "depending on which direction that government is moving."

The commission also called for U.S. support for black and multiracial organizations within South Africa, economic support for neighboring countries of southern Africa, particularly Zimbabwe, and stockpiling key minerals the United States imports from South Africa to lessen the impact of future interruption.

Franklin A. Thomas, president of the Ford Foundation and chairman of the Study Commission on U.S. Policy toward South Africa, summarized the group's findings and recommendations in a speech yesterday at the National Press Club.

Thomas said one key finding is that "a white minority South African government is, contrary to the beliefs of some, more of a danger to, than a guarantor of, our long-term interests because the government's intransigence promotes the growth of Soviet influence in southern Africa through increased political instability, rising levels of racial violence, and armed conflict."

He said another key finding, also at odds with the some beliefs, is that "if stoppages of key mineral exports from South Africa do occur, they are likely to be intermittent and of relatively short duration, whatever the political character of the government."