Since Mr. de Klerk initiated his reform program and began talks with the ANC and other black groups, most countries around the world have lifted trade and economic sanctions against South Africa.
If the process of reform were to end, so might South Africa's impressive progress in regaining international respect and much-needed foreign investment.
The United States lifted the Comprehensive Anti-Apartheid Act last year, removing sanctions on most trade and new investments.
Only Wednesday, speaking to businessmen in Nashville, Tenn., President Bush said he had issued a presidential order finding that "significant progress toward the elimination of apartheid has been made in South Africa."
The United States withheld any judgment of Mr. de Klerk's decision to call for a referendum yesterday, saying it was an internal matter.
"We continue to support fully the Convention for a Democratic South Africa process as the appropriate forum for discussions on South Africa's future. The specifics of the transition to a new constitution are for the people of South Africa to decide among themselves," said State Department spokeswoman Margaret Tutwiler.
Formal negotiations on a new constitution began in December between the government and 18 political organizations representing every racial group in South Africa. The second round of talks is scheduled to begin at the end of next month.
Mr. de Klerk has said he wants to hold the white referendum before that round begins.
Political reforms made by President F. W. de Klerk since he took office in September 1989:
APARTHEID LAWS: Repealed all major laws on separating whites and blacks, including segregation of residential areas and a ban on blacks' owning land in most of the country. Blacks still cannot vote in national elections, and education remains largely segregated.
OPPOSITION GROUPS: Legalized dozens of opposition groups, including the African National Congress and the South African Communist Party. Released black leader Nelson Mandela and other leading opposition figures from jail.
CONSTITUTIONAL TALKS: Is negotiating with the ANC and other groups on giving the vote to blacks. His goal is to establish a non-racial democratic state with protection for whites and other minorities from domination by the black majority.