CAPE TOWN, South Africa -- President F. W. de Klerk, who stunned the world two years ago with his plan to dismantle apartheid and give blacks a vote, reassured nervous whites yesterday that they will get a chance to veto new reforms.
In a speech opening the South African Parliament, Mr. de Klerk promised that a referendum would be held before any changes are made in the present constitution, which excludes the black majority from national affairs.
A top government minister, briefing reporters, said that all South Africans would vote in the referendum -- but if white voters rejected the reforms, "we would be forced to go back to the drawing board."
The suggestion that whites could delay or scuttle the reforms drew an angry response from Nelson Mandela, leader of the African National Congress.
"It is ridiculous in our view to embark on negotiations and then go and consult a particular ethnic group whose response might be negative," he told reporters in Johannesburg. "It suggests that if whites say no, then de Klerk would be bound to withdraw from negotiations."
More than 30,000 blacks marched peacefully through the streets of Cape Town after Mr. de Klerk's speech to demonstrate their opposition to the current Parliament.
The marchers were organized by the ANC, whose deputy president, Walter Sisulu, called for an interim government within six months to oversee the drafting of a new constitution.
Prior to Mr. de Klerk's speech, there was widespread speculation that this would be the last session of South Africa's segregated, white-controlled Parliament because the government has opened constitutional negotiations with black opposition groups.
But the speech suggested that Mr. de Klerk, who has dramatically changed politics in South Africa, believes he has gone as far as he can without getting a new mandate from the white voters who elected him in 1989.
His speech was directed at those voters, rather than at the international audience that seemed to be the target of his previous addresses to Parliament.
At the outset, Mr. de Klerk's reform program had the clear goals of winning world approval for his government and getting economic sanctions against South Africa lifted.
The goals have been largely achieved. After lifting bans on political opposition groups, releasing hundreds of black political prisoners and repealing the major apartheid laws, his government has won praise from across the world. Most foreign governments have also lifted the sanctions that punished South Africa for years.
"South Africa is looking back today on two years of unprecedented and dynamic change," Mr. de Klerk said. "It is noticeable and tangible in every sphere of life. Everywhere it has finally dawned upon everybody that we are experiencing a decisive period in our history."
Mr. de Klerk reaffirmed his commitment to "our goal of a free and democratic constitutional system based on the principle of representation for all."
But he made it clear that the white electorate was still decisive, as far as his government was concerned. In addition to an essentially white referendum, he said that the present white-controlled Parliament would also have to approve any constitutional changes.
"I wish to emphasize that only Parliament as constituted at present has the power to amend the Constitution," he said. Black opposition groups reject the present Parliament and government as illegitimate because they exclude the majority of the population.
Negotiations began last month aimed at completing the reform process, but there remain profound differences on how the process should proceed and what should be contained in a new constitution.
Mr. de Klerk favors a decentralized government with special protections for whites and a three-person presidency that includes leaders from the top three political parties. The ANC has proposed a strong centralized government based on the principle of one person, one vote. It has accused the government of attempting to build a white veto into the new constitution.
The negotiations are being boycotted by blacks on the far left, who say that the white government is not serious about handing over power, and by whites on the far right, who want a separate white state.
Mr. de Klerk rejected the idea of a sovereign white state within black-majority South Africa, saying that it had been tried and found to be "not practically achievable."
Apartheid was based on the idea that South Africa was a white state, ruled by and for whites, and that blacks were temporary residents allowed inside the country as laborers.