An extended shutdown of auxiliary cooling pumps, a major violation of federal regulations, contributed significantly to the events at the Three Mile Island atomic power plant that led to the nation's worst nuclear accident, the Nuclear Regulatory Commission was told yesterday.

Darrell Eisenhut, deputy director of the NRC's division of operating reactors, told the five NCR commissioners in Washington that Metropolitan Edison Co. had closed three auxiliary coolant pumps for maintenance "at least two weeks" before the accident and kept them closed until the accident occurred.

"This is a violation," Eisenhut told a stunned commission.

Harold C. Denton, the NRC's top man on the scene, told reporters in Middletown, Pa., yesterday, "There would have been an entirely different outcome it they [the pumps] had been operational, as they should have been."

He did not elaborate, but cited the pumps as one of the six problems in the first formal explanation of the accident to the NRC.

NRC regulations require that two sets of cooling pumps (three each) be available at all times whenever the nuclear power plant's uranium fuel is generating heat for electricity.

Eisenhut told the commission that NRC investigators were informed the three auxiliary cooling pumps were shut down for maintenance by workers at the plant. Eisenhut implied that officials of Metropolitan Edison had not informed the NRC of its move to maintain and repair the pumps in violation of the NRC rule.

"What we have," Eisenhut said, "is a statement from the operators (the workers on duty at the plant) that the pump valves were tagged as closed. They were tagged and isolated." Power plant operators put large colored tags on equipment out of service so workers will not mistakenly turn them on.

Reaction on Capitol Hill to the news that Metropolitan Edison had violated one of the stiffest of NRC's rules ranged from shocked disbelief to open anger.

"It completely baffles me as to how this could have happened." said Rep. Morris K. Udall (D. Ariz.), chairman of the House subcommittee on energy and the environment. "This is the sort of thing we will seek to understand during the course of our inquiry."

Udall told the Washington Post on Tuseday that he will open a "comprehensive" inquiry of the Three Mile Island accident to assess its impact on nuclear safety and regualtion.

"This kind of thing is a very strong argument for the kind of investigation the Senate should conduct," said Sen. Gary Hart (D.-Colo.), chairman of the Senate Public Works subcommittee on nuclear regulation. "I am going to propose that our subcommittee conduct just such an investigation."

If the NRC decides after a fuller investigation that Metropolitan Edison Co. violated its rules, it can assess no more than a $5,000 fine on the electric company "for each violation," At no time do its rules call for more of a civil penalty tha $25,000 for all violations in any period of 30 consecutive days.

Last May, the NRC sent Congress legislation recommending an increase in the single-violation penalty to $100,000 and the multiple penalty to $300,000. Congress had not passed this legislation.

Meanwhile, state officials in Pennsylvania said yesterday that Metropolitan Edison gained millions of dollars in a rate increase because they were able to get the Three Mile Island nuclear generator into operation quickly.

The utility lost one request for a rate increase last year because the nuclear plant did not come on line on schedule. Officials of the state Consumer Adovcate Office said that Metropolitan Edison narrowly squeezed under a state Public Utilities Commission deadline when it put the reactor on line Dec. 31 last year. Making the reactor operational enabled the company to get a $49 million rate increase from the state Public Utilities Commission with most of that increase granted because the reactor was operating. The PUC granted the rate increase last Thursday - one day after the accident.

"We have no evidence or proof to show whether the plant was put on line before it should have," said David Barasch, a staff attorney in the Consumer Advocate Office. "But there was no question that there was strong economic incentive for the company to get that plant on line fast."

Eisenhut told the commissioners yesterday that mainteance on the auxiliary pumps was being performed just before the accident took place.

"On the day of the accident at Three Mile Island, somtime between three and four in the morning," Eisenhut said, "there was maintenance being performed on the main feedwater system. At about 4a.m., the loss of condensate pump and feed pump caused the turbine to trip."

This was the start of the sequence of events that caused and contributed to the entire Three Mile Island accident. Had the three auxiliary pumps been on line when the two other pumps failed, the entire sequence of events might never have happened.

Besides the out-of-service auxiliary pumps, Eisenhut ticked off for the commissioners a chain of events that went on for many hours which caused the accident, sustained it and made it worse. Eisenhut identified six "major areas, where things went wrong and complicated the accident."

Among the six was the failure "in the open position" of a pressure relief valve that bleeds off water when the coolant pressure gets too high. At Three Mile Island the morning of the accident, this relief valve opened up to get rid of excess pressure and then stayed open so long that the pressure dropped below safe levels.

When an operator tried to close this stuck valve remotely, Eisenhut said, he couldn't do it. While he was trying to close it, there was a dramatic drop in the coolant pressure that dropped the water level in the reactor at least two feet below the top of the reactor core and damaged the uranium fuel for the first time.

Eisenhut was asked by the commissioners if the relief valve could have been manually closed. He replied: "In theory, yes. In practice, no." The relief valve is located at the top of the pressurizer in the reactor and is "inacessible" to workers any time there is trouble in a reactor.

Just after the relief valve stuck in the open position, pressure level indicators being read in the reactor control room were apparently erroneous.

The levels they read in the control room were higher than they really were, suggesting to operators in the control room that the top of the core was still safely under water.

The reactor's emergency core cooling system, its last-ditch method of flooding the reactor with water to cover and cool the 36,000 uranium fuel rods inside the core, was then turned off by the opeartor. How long it stayed off, Eisenhut said, is till unknown, but it stayed off long enough to keep the tops of the rods exposed and do further damage to the core.

The emergency core cooling system was turned off because the operator misread the pressure levels inside the core. The erroneous readings his pressure instruments were giviing him caused him to think the emergency cooling system was unnecessary.

"The operator may have read the instrument correctly," said Edson Case, deputy director of the office of nuclear regulation, "but this is not to say he should have relied on this instrument exclusively."

Eisenhut said the water level fell at least two feet below the top of the core, causing the fuel rods to overheat so badly their stainless steel cladding expanded, broke and relased radioactive fission products to the reactor vessel. Thermocuples measuring temperatures at the top of the reactor rose to 750 degrees and then climbed right off the scale.

The computer that prints out temperature readings in the control room began printing out "question marks." Eisenhut said, the sign that the computer has failed, the thermocouple has failed or the fuel rods are failing. Eisenhut said it is everyone's belief that the fuel rods were failing, meaning their temperature had climbed so high that the computer could no longer read them. CAPTION: Picture, Chairman Joseph Hendrie gets the NRC's first formal briefing on the Pennsylvania plant accident by staff aides Darrell Eisenhut, left, and Edson Case. By Ken Feil - The Washington Post