Tanzania's United Nations ambassador called on the United States last night to break economic, military and nuclear ties with South Africa to help force that country to end apartheid and white-minority rule.

The ambassador, Salim Ahmed Salim, who is serving as president of the U.N. General Assembly, was keynote speaker at the Washington Hilton Hotel for the third annual dinner for TransAfrica, a predominantly black lobbying group for political and social change in Africa.

"The time has come to dispel once and for all the illusion that 'business as usual' with South Africa will ultimately force change from within the land of apartheid," Salim said.

TransAfrica executive director Randall Robinson said the three-year-old lobbying group, which drew about 1,000 persons to the Washington Hilton Hotel last night, is beginning a campaign to "force the U.S. to disengage itself from South Africa."

TransAfrica previously has been involved in lobbying for the new government of Zimbabwe, formerly Rhodesia.

Salim praised the work of TransAfrica in pushing for change in Zimbabwe. The dinner was partly a victory celebration for the election of President Robert Mugabe's black-majority government in Salisbury.

Last night's dinner, which brought together many of Washington's leaders in business, politics and civil rights, including Mayor Marion Barry, was muted by concern throughout the audience over the still-unexplained shooting this week of Vernon Jordan, head of the Urban League who was shot in Fort Wayne, Ind.

In his speech, Salim warned that the change in Zimbabwe must be tempered by the fact that a white-minority government still exist in South Africa. The Zimbabwe breakthrough, he said, "represents what is achievable and what we should all be aspiring for" in South Africa.

Salim said that African governments clearly support negotiated settlements and peaceful transition to black-majority rule in Africa. But, he said, "the continued intransigence and repression of the apartheid regime" in South Africa and Namibia "could lead to a serious conflagration with wider implications for the whole world."