A picture of the Nuclear Regulatory Commission as a bureaucracy swamped in minutiae, with little time for pressing safety issues, emerged yesterday before the presidential commission investigating the Three Mile Island accident.

After hearing 5 1/2 hours of testimony from the five NRC commissioners and two key staffers, panel chairman John G. Kemeny said he was "shocked" and distressed.

Kemeny said the NRC commissioners "seem to have delegated a huge portion of safety to the staff below them and they are swamped with details of lesser priority."

Kennedy and other members of his panel also showed some dismay at learning that the Three Mile Island plant had been "grandfathered" out of coverage under tougher safety regulations adopted by the NRC in 1975.

He suggested that the March 28 accident at the nuclear generating station near Harrisburg, Pa., might not have occurred had those tougher regulations applied to the plant.

"I must confess I find that shocking," Kemeny told NRC staffer Roger Mattson after learning that, had the 1975 requirements been in force at the plant, they might have prevented radioactive gases from leaking into the air over the Metropolitan Edison Co. plant.

Mattson said the stricter rules for isolating a nuclear plant's containment building did not apply to TMI, which, like other plants, was exempted because it was under construction - even though it would not become operational until 1978.

Kemeny and other panelists suggested that the exemption was reflective of a larger issue confronting the NRC - that the commissioners allow their time to be frittered away on piddling detail, while major questions pass them by.

"My first inclination is to say it ought not be that way," Kemeny said, although he noted that his own experience as president of Dartmouth College has exposed him to the perils of bureaucracy.

As the day wore on, the commissioners sitting elbow to elbow at a long table in the hot glare of television lights, generally agreed with Kemeny and others who wondered if priorities might be askew at the NRC.

Another panelist, Theodore B. Taylor, a Princeton University physicist, told the five NRC commissioners that he was "very surprised at the lack of quantitative discussion" in the NRC meetings during the TMI crisis period.

Taylor said he gained that impression from reading transcripts of the meetings, which were almost continuous during the crisis as the NRC grappled with the threat of a hydrogen explosion inside the crippled reactor.

He said he found it "hard to understand" why the transcripts reflected little discussion of damage to the fuel rods or the implications of the growing amount of hydrogen inside the reactor.

NRC chairman Joseph M. Hendrie said he recalled that he and other commissioners had discussed those matters, but he acknowledged that he too, had been unable to find a record of the discussions in the transcripts.

Hendrie speculated that secretaries simply had not included those passages in the transcripts or that taperecording machines were not turned on when the issues were discussed.

But NRC Commissioner Peter Bradford told the presidential investigators that "there's more in the transcripts than you allow for." He said there was more discussions of the oxygen-hydrogen problem than of the damage to fuel cells because it presented a more immediate danger.

Victor Gilinsky said that he and the other NRC commissioners had not injected themselves aggressively into reactor safety questions, in part because of a tradition inherited from the old Atomic Energy Commission "of not delving into safety matters as deeply as other areas."

"When the NRC came into existence in 1975," he said, "the safety program was already set up. We had to build up in other areas, such as the nuclear safeguards program."

Commissioner Richard Kennedy agreed, saying in effect that safety was put on a back burner because the commissioners had to deal with the details of other new and pressing issues.

When Kemeny said he had been "horrified" to learn that the 1975 regulation changes didn't apply to the Three Mile Island plant, Gilinsky said, "I can go you one better. Licenses are issued without going before the commission. That ought to be changed."

Panelist Patrick E. Haggerty wondered how the five NRC officials break away from the fine-print detail of their jobs and, as he put it, "grapple with the future."

"With a certain amount of difficulty," said Hendrie. CAPTION: Picture, NRC's Mattson explains why Three Mile Island was exempt from 1975 rules. By Frank Johnston - The Washington Post