Would sanctions work to bring change to South Africa? Would they punish whites without helping blacks? Would they hurt blacks even more? Would they destroy rather than enhance American influence? To use the images in vogue this week, does White House refusal to impose sanctions enhance America's "flexibility," as the president contended on Tuesday? Or does it merely show a "lack of backbone," as Sen. Joseph Biden said a day later?

Some time ago, these would have been interesting questions, worthy of serious debate. Today, they are mostly beside the point. The problem is not the absence of flexibility. The problem is that no one believes Ronald Reagan gives two hoots in hell about apartheid.

Americans pushing for change in South Africa certainly do not count the president an ally in that struggle. South African blacks -- even those who, like Gatsha Buthelezi, oppose sanctions -- do not see the president as an enemy of apartheid. Even South Africa's government, whose power derives from the exploitation, inhumanity and denials of opportunity that comprise apartheid, sees the president not as an implacable foe but as a steadfast friend -- even if his own domestic politics sometimes require him to say some harsh things.

I know the president says he is opposed to apartheid. He said it at some length during his Tuesday speech. But he said it in almost precisely the terms I've heard so often from conservative Afrikaners: Apartheid must go, but it will go faster in a booming economy. Cripple the economy and blacks will suffer first and most. As Reagan put it, since black workers would be the first to lose their jobs, "the primary victims of an economic boycott of South Africa would be the very people we seek to help."

To which the obvious response is: What do you mean "we"? What has Ronald Reagan ever done that could fairly be said to have been motivated by a desire to help South African blacks? His spurious solicitude for the struggling blacks, which happens to square precisely with the mouthings of P. W. Botha, takes no account of recognized black leaders who continue to call, at risk of imprisonment for treason, for sanctions, for disinvestment, for something to show their oppressors that they can no longer count on American support.

That is the crying need: something to demonstrate America's seriousness about ending apartheid. A part of the reason that sanctions have taken on such importance as a token of that seriousness is Reagan's opposition to them. The black African leadership is crystal clear in its call for sanctions. But Reagan brushed aside these black leaders and instead invoked Alan Paton, the white "conscience of his country," who opposed disinvestment because "those who will pay most grievously for disinvestment will be the black workers of South Africa."

If the president wants a quotation in support of a position long since taken, the Paton one serves nicely. But if Reagan wants not merely to exploit that sensitive observer of the South African scene but to be instructed by him, let him listen to these words from Paton's 1959 book, "Hope for South Africa": "South Africa's strategic position and her vast resources of vital raw materials shrink into insignificance beside the question of how she solves her racial problems. The people of the outside world will be judged, in the eyes of South African leaders of the future, on how they measure up to this challenge in the next few years. Let the West take note."

President Reagan may not yet understand just who Paton had in mind when he wrote of "South African leaders of the future." But congressional leaders, including key senators of the president's own party, understand it clearly. That is why there will be sanctions.