THERE IS HEATED talk now about whether the demonstrations at the South African Embassy will go on and what tactics should be used and whether the protests and the arrests will accomplish anything and what the collateral effects may be and whether these activities can accomplish anything anyway, given the iron hold that South Africa's white minority has on that tragic land. These are hard questions, and good answers will be slow in coming.

What is striking already, however, is that the questions are being asked. It is happening as the direct result of demonstrations begun in this city barely two weeks ago. Do you not feel that something new is in the air? The demonstrations have imparted a new intensity and interest to an issue that earlier was off most Americans' screen. They have touched something that was there waiting to be touched. They have increased public interest in apartheid and diminished tolerance of it as a familiar, if terrible, constant. They have been a model of public expression, conducted so as to turn new attention on apartheid and bring new pressure to bear.

Do you think for one minute that President Reagan would otherwise have received Bishop Tutu, the South African Nobel Peace Prize winner? Just a few weeks ago apartheid was simply not on the presidential agenda, not something he had to devote his personal time to or prepare to talk about at a news conference. That is one measure of the change. Will it be so in two weeks, two months, two years? We offer no predictions. It is already evident, though, that the political system has a larger place available for this issue than many people had suspected. Liberal interest has been freshened, conservative interest stirred. Some signs of an altered political chemistry are there. Reaching into another society to affect social and political change takes care, skill and -- let's face it -- arrogance. It is tough to do, and it is tough to keep in mind that the only justification for trying is to make things better, especially though not exclusively for the particular people you are trying to help. South Africa is not ours to make over, but it can hardly be said that the United States has yet come near fully exploring the limits of its different sorts of influence. In particular, the possibilities of a conservative American administration remain largely untapped.

President Reagan has an unfortunate lack of evident empathy for the plight of South African blacks. He has a point, however, in stressing the uses of American business in expanding their opportunities. As defensive and rigid as he is about his policy, he was wise to say he would consider suggestions made to him by Bishop Tutu. In its domestic origins, his policy emerged from an atmosphere of low urgency. A higher urgency is being generated. Things need to "work," to ferment.

South Africa's release of some of its jailed prisoners -- in the group whose release has been a specific demand of the demonstrators -- is an early sign of one kind of response that an attitude of heightened American concern may bring. Mr. Reagan, having already made one statement on apartheid on Friday, popped up in public a second time to say that the release was a fruit of his policy. Others will argue about that but we will not. That's fine with us -- our next question to the president is this: Now that you have confirmed the principle that American policy can be counted on to produce concrete results, what is to be your next success?