U.S. sanctions against South Africa will remain in effect despite the announcement Thursday by President F.W. de Klerk that he is lifting emergency rule in three of the nation's four provinces, a State Department spokesman said.

''While we welcome this decision, this does not fulfill all our requirements for lifting of U.S. economic sanctions against South Africa," said the spokesman, who asked not to be identified.Other requirements that must still be fulfilled under the legislation that imposed the sanctions include the repeal of remaining apartheid legislation, the release of remaining political prisoners and an end to emergency rule in Natal, the province where it will remain in effect, the spokesman said.

As a result, companies not doing business in South Africa now would be prohibited from doing so, she added.

On the other hand, the United States continues to believe that American companies already doing business in South Africa play a positive role there and should remain, she said.

Black nationalist leader Nelson Mandela welcomed the move, calling it "a victory for the people of South Africa as a whole."

Before Mr. de Klerk made his announcement, Mr. Mandela said he would go on campaigning for continued international sanctions against South Africa even if the state of emergency were lifted.

"There is no announcement that will make a difference. If the government decides to lift the state of emergency, it will represent a victory for the people of South Africa, but it cannot change my perception," Mr. Mandela said earlier.

"Once the process of democratization is fully under way, only then would it be appropriate for the U.S. and other countries to lift sanctions," said a congressional staffer.

Stephen Davis, a senior analyst with the Washington-based Investor Responsibility Research Center, noted that South Africa is still far from reaching a final settlement on its future, including a consensus on the economic shape of a post-apartheid society.

Therefore, he said, "It's likely that foreign corporations, in particular U.S. corporations, are going to want to see much more concrete results before they consider investing in South Africa."

Mr. Davis said the debate over what kind of economic system South Africa should have in the future has just begun.