COLUMN LEFT/ GEORGE BLACK : One Reformer Meets Buzzsaw, One Doesn’t : Bush asks for absolute proof from Gorbachev, but makes no such demand on De Klerk.

At the London summit of the Group of Seven nations, Mikhail Gorbachev was subjected to Star Chamber treatment. He was grilled and cross-examined, prodded and pinched like a piece of fruit in a grocery bin.

And at day’s end, the verdict was the same as it had been at the Houston summit a year ago. The Germans and the French, seeing the prospect of social collapse next door, favored direct financial aid. The United States, with Britain and Japan in tow, saw the Soviet economy as a rat-hole and refused to throw good money after bad. Beneath all the kind words and the promises of associate membership in the International Monetary Fund, George Bush’s message to Gorbachev was simple: Show me absolute proof that your reform process is irreversible.

The curious thing is that no such burden of proof had been demanded a week earlier from South African President Frederik W. de Klerk. In announcing the end of U.S. sanctions, Bush declared that events in South Africa were evidence of “irreversible change.� Granted, the last year has been historic: Nelson Mandela released, the African National Congress unbanned, the main legal pillars of apartheid scrapped. But irreversible?

As Mandela himself was the first to recognize, the U.S. legislation was written in such a way that sanctions were bound to be dropped the moment De Klerk was in technical compliance. Even so, De Klerk emerges with a triumph that few white supremacists could have imagined, ending South Africa’s isolation overnight without surrendering white dominance of any of the country’s political institutions.

De Klerk seems, in fact, to have learned a great deal from the way in which the United States dismantled its own version of apartheid. And he surely shares Bush’s dream of creating a land in which a South African Clarence Thomas will be allowed to climb to the top and then preach against any institutional redress that might help others to do the same.

The 1986 state of emergency has been scrapped, but the regime may still assume extraordinary powers in “unrest areas�--of which there are currently nine, thanks to the murderous activities of Chief Mangosuthu Gatsha Buthelezi’s Inkatha. The Group Areas Act is gone, but a new law allows existing “norms and standards� to be maintained in white residential areas. Good-faith talks about future political reform have not yet begun, and both De Klerk and Buthelezi have rejected the assembly that would accurately represent the country’s various political forces. Nothing, in other words, is “irreversible.�

The most unseemly aspect of abandoning sanctions is the matter of South Africa’s remaining political prisoners. The Bush Administration accepts the De Klerk regime’s definition of a political prisoner, and agrees that all have been released. Amnesty International and Africa Watch believe that around 850 are still being held.

What makes this more than a technicality is the status of 164 prisoners held in the nominally independent homeland of Bophuthatswana. Here, the dispute is not over whether these detainees were guilty of violent crimes; most are ANC members charged with treason after a coup attempt was crushed by the South African Defense Forces in 1988. Worse, by accepting De Klerk’s assertion that these prisoners do not fall under South African jurisdiction, the United States accepts the legitimacy of an autonomous homeland, and thereby the entire legal fiction of the apartheid state.

Events in the Soviet Union over the last year have been every bit as momentous as those in South Africa. Boris Yeltsin, who resigned from the Communist Party only a year ago, has been elected president of the Russian Republic on a platform of privatization and free enterprise. Gorbachev has ended his brief tactical alliance with the troglodytes in the Soviet security Establishment and made common cause with Yeltsin. A new democratic opposition group has emerged, led by figures of the stature of Alexander Yakovlev and former foreign minister Eduard Shevardnadze. And now Gorbachev has come cap in hand to London. The process of democratic reform may be no more irreversible than the establishment of a multiracial democracy in South Africa. But is it any less so?

Irreversibility, in the end, lies in the eye of the beholder. For more than 40 years, U.S. policy-makers have been less hostile to South African apartheid than to Soviet communism. And in Bush’s eyes, De Klerk still offers the glass half-full, Gorbachev the glass half-empty.