President Bush yesterday effusively praised the "efforts and courage" of South African President Frederik W. de Klerk and declared that the process of dismantling apartheid in that nation is now "irreversible."

Speaking in a South Lawn ceremony at the conclusion of the first White House visit by a South African head of state, Bush also pledged that he would not alter the conditions for lifting economic sanctions.

"We believe the process of change in South Africa is irreversible, a fact that we will bear squarely in mind as we consider issues in the future," the president said. He added that the conditions that must be met before congressional legislation imposing sanctions can be lifted "are clear-cut and are not open to reinterpretation, and I do not believe in moving the goal posts."

After the White House meeting, South African officials expressed broad pleasure at what they described as Bush's vote of confidence. South African Foreign Minister R.F. "Pik" Botha noted, "We feel that {whatever} has separated the United States and South Africa, that separation has been crossed."

Bush's reference to the irreversibility of reforms, he said, "is the element the European governments have been looking for" in beginning the process of reestablishing economic ties with South Africa. The European Community and Britain, among others, have demanded "evidence of profound and irreversible change" as a condition of lifting their economic sanctions and Bush's use of that language was seen by the South African officials as a key international signal of the faith the administration has in de Klerk's government.

De Klerk said that Bush's meeting with him and the president's assertion of the irreversibility of apartheid's demise was "very important" for his efforts to bring his nation back into "the international community."

De Klerk, who has declared the inevitability of the end of apartheid since he freed African National Congress leader Nelson Mandela from prison in February, pledged yesterday, "We will not turn back." From new "negotiations there will come about a new constitution that will offer full political rights within the framework of internationally-acceptable definitions of what democracy means."

"There will be a vote of equal value for all South Africans," de Klerk said in a statement the White House interpreted as an endorsement of the one man-one vote principle.

In an interview on the "McNeil/Lehrer NewsHour" last night, de Klerk said the statement did mean that one man's vote was equal to any other man's vote, but he insisted, without discussing specifics, that some means to "protect the rights of minority" whites would have to be part of the system.

While Bush was stating that "all Americans recognize that President de Klerk is courageously trying to change things," some 200 protesters outside the White House disagreed. Randall Robinson, executive director of the anti-apartheid group TransAfrica, said that "the pillars of apartheid are still in place" in South Africa and that by granting de Klerk "such legitimacy, President Bush is turning back the very progress that was made by the sanctions he opposed."

Bush, without specifically mentioning the black township violence that has taken more than 750 lives since August, said the government there "has a special responsibility to maintain order." In an apparent reference to the ANC, he added, "But all political parties and groups

have a special responsibility to support the process of peaceful transition."

In his remarks, de Klerk called the violence "totally unacceptable" and assured Bush that he has "taken steps in an impartial manner through the use of our security forces to curb the violence." He insisted he was "as anxious as you are" to lift the state of emergency in the province of Natal. Lifting of that state of emergency, as well as the release of political prisoners, are two of the five conditions for ending sanctions that have not been met.

White House officials said yesterday they expect all the conditions to be met early next year. Herman Cohen, the assistant secretary of state for the region, said Bush "is prepared" to lift sanctions but "is just unable to do so" until the final conditions are met.

Staff writer Dana Priest contributed to this report.