JOHANNESBURG, SEPT. 22 -- Frederik W. de Klerk, who arrives in Washington on Sunday for talks with President Bush, appealed to Americans today to look at South Africa through new lenses and accept that he "means business" in his stated commitment to negotiate a new non-racial constitution.

But the South African president travels to the White House at a difficult time for his government at home amid the first signs of a souring of his relations with the African National Congress.

Speaking to American reporters hours before his departure, de Klerk said many Americans were "still looking at South Africa through glasses they should have discarded by now."

"There's really a great challenge to change the image which has burned into their minds by years and years of images flashing across their TV screens and to get the wider public also to realize that things are happening," he said.

De Klerk is scheduled to meet Bush on Monday morning, but the South African leader said he would not have "hat in hand" or ask that congressionally imposed sanctions now be lifted.

"I think that will take care of itself as South Africa proves -- which we intend to do and which we have already started to do -- we mean business," he said. "There will be a new constitution, there will be negotiation. Time is of the essence. Therefore, there won't be any dragging of the feet whatsoever."

U.S. officials said the main point of de Klerk's visit was to give him the opportunity to establish a personal rapport with Bush, regarded as particularly important because of the American president's style of foreign policy-making and penchant for diplomacy by telephone.

A senior South African official said de Klerk was aware that some protest demonstrations -- aimed partly at his handling of the recent upsurge of black township violence that has taken more than 750 lives -- were being planned during his two-day working visit to Washington. But he dismissed their organizers as people trying "to keep the old images {of South Africa} alive."

{The Congressional Black Caucus announced Saturday that it canceled a scheduled meeting with de Klerk "in response to recent developments in South Africa and after extensive consultation with anti-apartheid activists."}

De Klerk will be the first South African president or prime minister to make an official visit to the United States since Jan Smuts in 1946. His visit already has been postponed twice because of congressional opposition to its timing.

Both governments have devoted a lot of diplomatic effort to smooth the way this time for as non-controversial a visit as possible, seeking deliberately to uncouple it from any administration decision on easing sanctions, according to both U.S. and South African sources.

Assistant Secretary of State Herman Cohen met here recently with Nelson Mandela and other ANC leaders to assure them that the administration has no intention of lifting sanctions at this time, the sources said.

Congressional leaders, who also were consulted at length about de Klerk's visit, felt the time had finally come, as one reportedly put it, "to meet the other guy," alluding to Mandela's visit to Washington in June and referring to the man who since February freed Mandela, legalized all anti-apartheid groups and initiated a negotiating process still in its formative phase.

But the current township violence has raised questions about de Klerk's ability, or willingness, to act decisively to stem the bloody factional fighting and indiscriminate killings that have taken place in the past two months around Johannesburg.

The ANC National Executive Committee issued a statement Wednesday accusing de Klerk of pursuing a "two-track policy," accepting negotiations while "devising strategems to weaken the ANC and other democratic formations."

The executive committee was particularly critical of the government's Operation Iron Fist, declared last weekend to put an end to the violence that has come to be marked increasingly by incidents of unknown groups killing innocent bystanders with machetes, knives and guns on commuter trains and in the streets of Johannesburg.

The ANC has said variously that the crackdown, which includes a heavier police and army presence in the troubled areas, has come too late, is excessively burdensome to the black population or is intended to restrict political activity and reintroduce a state of emergency "by guile."

De Klerk apparently has been stung by the criticism, particularly the ANC's charges that he has acted in "bad faith."

Asked why the government had waited so long to crack down, the senior South African official said it suddenly found itself faced with a "new dimension to the violence," one in which small numbers of "desperados" were shooting down innocent people at random.

"A different tactic is being used which hasn't been used widely before, and that is a typical terrorist tactic of just instilling fear and panic among the masses on a train or on a street corner irrespective of who gets attacked," he said. "That hasn't been the character of the violence in June, July and early August," when it was based on ethnic and factional fighting, he added.

The official said the government had no hard evidence as yet that "a sinister third force" was responsible for these killings, but added that the theory that white right-wing elements opposed to de Klerk's reforms were involved was not "a far-fetched possibility."

De Klerk's aides today distributed a statement in the president's name saying he was ready to hold high-level meeting with the ANC or other groups to discuss their grievances against the new security measures. In it, he appealed to such groups to enter into private talks with the government rather than indulge in "public accusations and debate."