In this space a few days ago we talked about missed opportunities, the kind that are now available and for which there is going to be much regret and nostalgia a short time hence when people realize those opportunities are no more. The subject that day was deficit reduction. The subject today is South Africa. But the underlying principle is the same. There is a slim, remote last chance to try to reach a peaceable and just resolution -- but it is being kicked away.

We thought of it the moment we saw the picture and read the account of that brave man, Bishop Tutu, coming between the South African police and black mourners to prevent a bloody confrontation the other day. "Please allow us to bury our dead with dignity," he said. "Please do not rub our noses in the dust. We are already hurt; we are already down. Don't trample on us. We are human beings; we are not animals. And when we have a death, we cry like you cry." If things proceed as they have been in South Africa and if the government continues its present cruel and senseless policies, there will come a day when it will sorely wish it had only to yield such things as Bishop Tutu has been asking -- political freedom, dignity and decency -- and that there were such people as Bishop Tutu with whom to negotiate.

The fact is that over the years, Pretoria has obdurately and suicidally refused to recognize or credit legitimate, peaceful civil protest on the part of nonviolent blacks. It met such protests with violence, repression, gunfire and lockups. It has done everything it could think of to weaken the hand and undermine the leadership of those whom it should devoutly wish to be the leaders of the restless, growing black resistance to apartheid. Most recently Prime Minister Botha declined a meeting with Bishop Tutu. The moderate leaders of Desmond Tutu's generation are being defied and often ridiculed by their own young for the scant results, as the younger ones see it, of their moderation and insistence on nonviolence. The trend in that unhappy land is such that you must believe that in a short time white South Africa will look back with real regret on these lost days and vanished opportunities.

In this country we have reached a policy stalemate. Within the president's own party there is some objection to his administration's moving toward a stronger condemnation of apartheid in general and of the South African government's misguided new wave of repression in particular. Outside his administration, on the left and to a considerable extent in the center as well, there is increasing dissatisfaction with the so-called "constructive engagement" policy of the past several years, a belief that it has yielded little. Congress, before it left town, sent the president a bill that would impose relatively modest sanctions against South Africa. Mr. Reagan has spoken of vetoing it, but is leaving the matter open for discussion.

We have never favored the disinvestment program that many have advocated over the years, believing it would hurt its intended beneficiaries, South Africa's blacks. The current legislation seems to us to contain much milder and more reasonable measures than what was once in the works. It also seems to us that, despite all the argument that has been going on, there is a fairly broad general consensus available on the kind of pressures that should be brought to hasten the end of racial repression in South Africa, and that this consensus extends from within the Reagan administration to many of the critics on the outside. There is common ground there that could be seized upon, so that a single, strong American policy could be fashioned.

Nothing is more important at this time. This country must not, at so critical a moment, descend into an internal, self-absorbed political squabble over what we should be doing. The American opportunity is now, and it may not come again. The country must speak with conviction and a clear voice and use its influence to press the South African government away from a mad and morally squalid course. It is possible for the administration and Congress to agree: they are not that far apart. Bishop Tutu speaks and acts for those who do not wish violence, but who insist on freedom and decency. That is what the United States should be for.