While South African President F. W. de Klerk was inside the White House, hoping to persuade President Bush that major change is underway in his country, 150 protesters were outside, hoping to make the point that, for South African blacks, very little has changed.

Both were right.

In terms of the prospects for racial peace and political justice, South Africa has made a quantum leap. As recently as a year ago, only die-hard optimists thought there was any chance of avoiding full-scale racial war. Today, everyone believes that, with a few timely concessions and a little luck, South Africa can finally dispose of apartheid and move to some negotiated arrangement for political power sharing.

The difference in outlook is largely attributable to two men: Nelson Mandela, who spent more than a quarter of a century as the world's most celebrated political prisoner, and de Klerk, who released him early this year.

Mandela has shown both the charisma and (surprisingly) the stamina necessary to unite the foes of apartheid, with the major exception of Zulu Chief Gatsha Buthelezi, with whom he has scheduled a meeting. De Klerk, in defiance of his country's powerful right wing, has made essentially all the concessions demanded by blacks as a necessary condition to negotiations.

Mandela and other major political prisoners have been released, the African National Congress and 32 other outlawed organizations have been unbanned. The official "state of emergency" remains an obstacle, but not an insurmountable one. Racial accommodation really does seem a reasonable prospect.

But for ordinary blacks in South Africa, little has changed. They remain powerless, largely propertyless and voteless. Their schooling and health care remain abominable, and their oppression by the white-run security forces continues unabated. They alone, among South Africa's racial groups, remain without representation in the government.

In addition, serious problems remain, including the recent kidnapping and assault charges against Mrs. Mandela, political opposition by right-wing whites and inter-tribal killings by blacks, particularly in Natal. Some of the killing is the result of long-standing animosity between Buthelezi's Inkatha and non-Zulus in the region, and some has been attributed to what has come to be called a "sinister third force" -- presumably a malign conspiracy between racist elements of the security forces and their black stooges.

Still, it's hard not to believe de Klerk when he insists that the changes underway are "irreversible."

De Klerk, whose visit here is the first by a South African president since the 1946 visit of Jan Smuts, told a breakfast meeting of journalists that there is "a growing commitment by a growing number of leading figures in all spheres to a negotiation process from which must flow peaceful solutions, a broad consensus with regard to a new constitution and full participation within that new constitution."

For the first time, he implied his willingness to accept a one-man, one-vote arrangement, at least for the lower house of a bicameral legislature, though he naturally insists on political protections for the white minority.

He listed as the major remaining problems (aside from the country's shattered economy) the need for major investment in black education ("We need to build one new average-size school per school day"), the continuing internecine fighting between blacks in Natal and the debate over the form of the government and the shape of the economic system.

He indicated that he has no doubt that these problems can be resolved.

If they are, it will be because of the extraordinary character of de Klerk and Mandela, and the extraordinary bond between them.

Even while recently criticizing de Klerk for being less than candid with him regarding his internal opposition and the treachery of the defense forces, Mandela said he still regards de Klerk "as a man of integrity -- and I think he feels the same way about me." "We have developed enormous respect for each other," he said, "and we talk very frankly. I can call him at any time. I can get him out of bed or pull him out of cabinet meetings. We have that kind of personal relationship."

That personal relationship, which de Klerk also described to journalists this week, may be the key to South Africa's racial dilemma.

The unanswerable question, about which de Klerk is known to worry, is whether this odd couple has the time to work things out.

As de Klerk recently told a European visitor, he has only three years before he has to face his party (and little likelihood that he would be reelected), and Mandela, 72 years old and ailing, may not have much longer than that to live.

His poignant conclusion: there's no time for the temporizing and game playing that has marked previous regimes if South Africa is to save itself.