SOME 200,000 PEOPLE gathered last weekend for the largest anti-nuclear rally ever held. The speakers called for a variety of different measures, but most demanded a ban on further construction of nuclear power plants and the closing of plants already in operation. Nuclear power became a symbol, or symptom, of various ills ranging from an overcentralized economy to a failure to pursue genuine arms control.

Unhappily, such rhetoric merely tends to confirm the views of the most fervent nuclear advocates that nothing is wrong with nuclear power except, in the words of one of them, "the critics, the courts, the bureaucracy, the press and the politicans." Neither view is right, and neither helps resolve the real and pressing problems associated with nuclear power.

Nuclear energy now provides about 4 percent of the nation's total energy, and 12 percent of its electricity. That doesn't sound like very much, but closing the country's 71 existing nuclear plants -- which represent investments in the tens of billions of dollars -- would have severe economic repercussions. In some regions the results would be devastating. Therefore, closing plants that are operating or partially constructed is both unlikely and unreasonable without clear evidence that they are unsafe and that their deficiencies cannot be corrected. The various commissions and investigations analyzing every aspect of the Three Mile Island accident may come up with such evidence; but from what has come out so far, that seems remote.

The longer range future of nuclear power is a different matter. The United States has had a de facto moratorium on new nuclear plants for several years -- utilities have simply not ordered any new reactors -- and this will continue at least until all the questions raised by Three Mile Island have been resolved. Nuclear power will therefore not experience the tremendous growth its advocates have predicted and its critics have feared. Nor will it substantially lessen the country's dependence on imported oil. Nevertheless, it can make an important -- perhaps vital -- contribution to a balanced energy budget during the hoped-for transition to reliance on renewable energy resources.

The real issues that have to be faced, if nuclear power is to play this modest but significant role, are reactor safety and the management of nuclear waste. It is here that nuclear skeptics could most usefully focus their attention. In particular, the government's continuing failure to come up with a waste-management plan that is technically sound and politically acceptable casts a long shadow over nuclear power's future. Nearly two years ago the president launched a major interagency study of this problem. The group's draft report, which was circulated for public comment months ago, amply testified to the magniturde of both the technical and political uncertainties. Though generally well received, the report disappeared back into the maw of the bureaucracy and hasn't been heard of again. Whatever the outcome of that particular effort, the country needs a widely acceptable nuclear waste policy, and soon. If one cannot be developed, the future of nuclear power will take care of itself.