THE SUPREME COURT lost no time in reversing a strange decision of the U.S. Court of Appeals in a case involving the reopening of a nuclear reactor at Three Mile Island. The lower court opinion, issued last May, held that an undamaged reactor at that complex could not be restarted until the Nuclear Regulatory Commission had considered evidence on the psychological effects of the decision on the residents of surrounding communities. This week, in a unanimous opinion, the Supreme Court held that such an interpretation of the National Environmental Protection Act went far beyond the intent of Congress.

That law requires all federal agencies to assess the environmental impact of proposed actions and to report any "adverse environmental effects." Certainly, the operation of any nuclear plant will to some extent affect the environment, and some part of its effect will be detrimental. The TMI plant, for example, emits some low-level radiation, increases fog in the Harrisburg area and releases warm water into the Susquehanna River. It may also create anxiety in the people living near the plant and in their friends and relatives throughout the country. This stress can be caused by quite genuine fear of the reactors or by strong disagreement with a government decision, made through a democratic process, to allow its construction.

The Supreme Court holds that it is the former set of consequences--those that may affect human health by causing changes in water, air or land-- that Congress intended to be considered. As for risk of psychological effects, the Supreme Court was clear: "Time and resources are simply too limited for us to believe that Congress intended to extend NEPA as far as the Court of Appeals has taken it."

Imagine the consequences if the risk of psychological stress were deemed an environmental factor that had to be taken into account before the federal government could take any action. Each agency, as the court points out, would have to expend considerable resources developing psychiatric expertise to assess these claims. Lawsuits to stop construction of jails, Job Corps training centers and low-income housing because of neighborhood fears of increased crime have failed in the past. They would be given new life under a ruling that expanded the definition of environmental impact to include risk of stress. Policy objections to federal programs and decisions would be raised, not only in the political forum, but also as environmental factors to be considered in the federal regulatory process.

Common sense should have led the Nuclear Regulatory Commission to hear all objections of persons opposed to reopening TMI. The failure at that site was a frightening and disruptive experience for those who live in the area. But there is a significant difference between a policy that may be prudent in a specific situation and one Congress has made mandatory in all cases. The distinction was clear to the Supreme Court, as it should have been to the court below.