FOR POLICY AND POLITICS, the consequences of the accident at the Three Mile Island reactor will clearly be tremendous. It is an accident that, by every principle of design, should not have happened. Inevitably, it raises questions not only about this reactor but about the 71 others in operation around the country-and the 90 further reactors under construction. Does this accident require the country to change its ideas regarding the chances of serious trouble in other places? The immediate issue is not how to build the next generation of reactors, but whether to keep using the present ones.

Those citizens who are not nuclear engineers will feel a sense of sharp exasperation at the incomplete and sometimes conflicting explanations currently offered from Three Mile Island. Part of the reason is simply that no one yet knows precisely what went wrong inside the reactor. There's a certain analogy to an airplane crash. Part of the story can be inferred at once, but the rest of it requires a meticulous examination of the wreckage. In this case, the specialists may have to wait a matter of weeks before it is safe to enter the reactor and inspect the damage at first hand.

The utility, the Metropolitan Edison Co., said with irritation that its press conference yesterday would be the last on the subject. That's just as well. Its statements are inevitably clouded by the thought of financial liabilities. The federal Nuclear Regulatory Commission has the primary responsibility here for public explanation, and so far it has responded pretty well. The commission knows that in years past the federal government itself has contributed hugely to laymen's suspicions of nuclear energy by its pollyanish evasions in responding to unwelcome questions. In the present test, the commission is going to have to set an Olympic record for candor and painstaking rectitude if it wants its judgments to be believed.

Speaking of consequences, what do you think might be the political consequences of a ban on air-conditioning in a city with a climate like Washington's? That's not a large probability at the moement, but neither is it impossible. Most power companies have large margins of capacity over even their peak levels of demand. But if the reactors are going to be shut down for review, those margins are going to shrink drastically. It's time to start thinking about the things that we as a society use electricity for, and, if necessary, what might be turned off.

It has been an unpleasantly instructive week. Two days before the accident at the reactor in Pennsylvania, OPEC had met in Geneva to discuss the price of oil. It now is evident that the OPEC meeting has resulted in prices that will be much higher than seemed likely at first. Additional countries have joined the North Africans in their campaign for enormous and immediate increases. The Saudis, in their usual elliptical manner, murmured suggestions of possible reductions in their production, which has become crucial to the world's economy; once again, they urged the United States to cut back imports. But if the reactors are shut down, as the weather turns warmer and air conditioners switch on, the rising load will fall mainly on oil-fueled generators. The strain in one part of this country's energy system exacerbates the strains in other parts.

There are larger political decisions to be made here than the NRC's engineers and regulators can properly be expected to approach. It would be helpful to the country to hear President Carter address the choices now emerging. It would be particularly helpful if Mr. Carter were to rise above the technical and administrative quarrels that usually preoccupy him, and address the larger principles of policy here-those principles that, taken together, comprise the ethnics of risk.

There is one kind of danger, perhaps larger than most Americans previously thought, in continuing with nuclear power. There is another kind of danger, perhaps to different people, in turning to other power sourcces or to none at all. Americans are not likely to be ablt to resolve the technical questions until they somehow find their way past Three Mile Island to a clearer sense of public values.