The Nuclear Regulatory Commission has decided that psychological stress and community fears among the Pennsylvania residents should not be considered in deciding whether to restart the undamaged Unit One reactor at Three Mile Island.

The commission split 2-2 on the question Friday, but said that vote "constitutes an effective denial" of citizens' petitions. Residents of the Middletown, Pa., neighborhood around Three Mile Island testified in recent hearings that the accident last year at Unit Two had left them fearful of any nuclear power plant, and that such fears were a social cost that ought to be considered in the NRC debate over whether Unit One could restart.

The commission has made a special case of Unit One, which was not damaged in the accident, partly because of community worries and also because it is a virtual twin of Unit Two where the malfunctions occurred.

In four separate opinions, the commissioners agreed that stress is an important consideration at Three Mile Island, but split on how to deal with it. Chairman John G. Ahearne said, "The best way to decrease such stress is to ensure the plant is safe if it is approved for operation."

Commissioner Joseph Hendric, opposing admission of stress considerations, agreed with Ahearne and added, "The actual level of risk is essentially irrelevant to the psychological stress claimed to be suffered . . . . There is no way to allay that fear except not to build or operate the reactor."

Besides, he added, "Congress has already decided that the country is to have a nuclear power program even if it makes some people uneasy."

Commissioner Peter A. Bradford, arguing in favor of considering stress, said citizens' fears would only be increased if the NRC refused to discuss them. "One need not fully share this public skepticism to find it understandable," he said. The NRC's technical judgements "and this agency inadvertently helped to bring about the accident. People near TMI who know little else about the NRC know that. Their lack of belief in the NRC is a basic source of the problem."

Don Hossler, chairman of the Middletown group called People Against Nuclear Energy, which filed the petition, said the decision means the NRC has chosen to ignore studies finding high stress levels in the area.

"Just because the NRC thinks a technical decision is sound doesn't mean the people's trust increases any," he said. "We were told this accident wasn't possible in the first place."