Sen. Richard G. Lugar (R-Ind.), chairman of the Senate Foreign Relations Committee, said yesterday that he is "ready to consider" immediate economic measures against South Africa.

Calling the situation there "extremely grim," Lugar indicated he may be prepared to abandon his plan to wait two years to determine whether South Africa has made "significant progress" toward ending its policy of racial separation.

Lugar's shift represents a serious blow to the administration's uphill struggle to persuade Congress to withhold punitive economic measures against South Africa.

While the administration had not backed the Lugar bill, with its built-in delays, officials have said there is "much in it" that they could support.

Lugar said further that he is ready to consider proposals for sanctions other than the four listed in his bill, cosponsored by Sen. Charles McC. Mathias Jr. (R-Md.) and Senate Majority Leader Robert J. Dole (R-Kan.).

His proposals include consideration of a ban on new U.S. investment and loans in South Africa and a prohibition on both the import of South African gold krugerrands and the export of U.S. computers to the white-run government.

Other measures being proposed include banning imports of coal and uranium from South Africa, prohibiting the sale of U.S. nuclear-related technology or goods and reducing the number of South African consulates here.

Lugar made his statement during a hearing that included testimony from Altanta Mayor Andrew Young and TransAfrica Executive Director Randall Robinson in favor of sanctions, and three U.S. representatives of business strongly opposing them.

Michael A. Samuels, a vice president of the Chamber of Commerce of the United States, urged the Senate committee not to approve legislation "forcing disinvestment or outlawing new investment" by U.S. firms because, he said, this would eliminate "a positive force for change within South Africa."

He said that the chamber also opposes making the Sullivan principles mandatory because it is "not appropriate" for the U.S. government to try to dictate how U.S. firms operate overseas.

These principles, named after the Rev. Leon Sullivan of Philadelphia, spell out a code of conduct aimed at improving working conditions for nonwhite employes of U.S. companies operating in South Africa.

The Lugar-Mathias-Dole bill would make the principles mandatory and provide for punitive measures against violators.

Speaking on behalf of the National Foreign Trade Council, Paul T. Murphy, vice president for government affairs, concurred with Samuels, arguing that making the principles mandatory would amount to making U.S. firms "agents of U.S. foreign policy."

Lugar said that he had invited "well over a dozen" large U.S. companies to testify on the economic sanctions legislation, but that only the Chamber of Commerce, the Foreign Trade Council and Sentry Insurance Company had accepted.

Young, former U.S. ambassador to the United Nations, argued that it is important for the United States to act now before it is too late, to "send a strong message" that this nation does not condone the "drift" in South Africa's apartheid policies.

Imposing sanctions, such as a ban on new U.S. investment and loans to South Africa, he said, would provide the kind of "outside idealistic authority" needed to convince the South African government to "change quickly in order to avoid chaos and bloodshed."

Robinson urged the United States to pass what he termed the "very moderate sanctions," to make an effort to convince South Africa's white rulers to change the apartheid system and negotiate with the black majority.