The Nuclear Regulatory Commission yesterday levied at $155,000 fine, the largest in its history, against the company that operated the Three Mile Island nuclear power plant, and held open the possibility that the company's license to operate the plant will be revoked.

"The action we have taken against the Metropolitan Edison Co. [operator of Three Mile Island] could lead to actions that would modify, suspend or revoke their license," Victor Stello, director of the NRC's Office of Inspection and Enforcement, told a news conference yesterday. "These are matters that are definitely being considered."

Leonard Bickwit, general counsel to the NRC, revealed that four members of the five-member commission took a vote last week on whether to revoke Met Ed's license. The result was a tie, resulting in no action.

"Commissioners [Peter] Bradford and [Victor] Gilinsky voted for revocation," Bickwit said, "while commissioners [John] Ahearne and [Joseph] Hendrie was opposed. Commissioner [Richard] Kennedy was away at the time, which meant with the tie vote that the motion to revoke the license failed."

The staff of the NRC gave notice to Met Ed that is has levied the $155,000 for seven violations of agency rules. The NRC staff said is specified violations by Met Ed that could have run the fine to $725,000 but that the Atomic Energy Act limits civil penalties for any single violation in a 30-day period of $25,000.

Six of the violations called for a $25,000 fine, and the seventh for $5,000 which brought the total to $155,000.

"This is the largest civil penalty ever proposed by the NRC staff," Stello said. "I beleive the actions we are taking carry a message to the [nuclear power] industry that is loud and clear."

Metropolitan Edison has 20 days either to protest the action or to pay the $155,000.

Stello also made it clear that yesterday's action may not be the end of the NRC staff's moves against Met Ed. He said the staff is studying the possibility of revoking the utility's license to operate the Three Mile Island nuclear plant.

Still under investigation is why Met Ed failed to notify the NRC immediately of the high radiation readings (10 to 40 rem per hour) inside the Three Mile Island containment building, of the superheated temperatures inside the damaged nuclear core and of the indication of a hydrogen explosion inside the containment.

All three things were known to Met Ed on the day of the accident last March 28, but we not reported to the NRC until two days later. The high radiation, the high explosion were signs that the nuclear core was badly damaged and presented the clear danger of a meltdown that could have forced a massive evacuation.

"We are trying to determine if these delayed notifications were willful," Stello said. Added General Counsel Bickwit: "Revocation [of the Met Ed license] is a possibility."

Stello said the NRC staff originally identified 36 separate instances in which Met Ed appeared to violate NRC regulations in the Three Mile Island accident, but narrowed the list to 17.

"We removed 12 that we felt were not important or where the plant operators took actions that were reasonable," Stello said. "We combined another seven that related to the same issues."

Of the six violations for which the maximum fine of $25,000 was levied, Stello said the two most serious were the closing of a series of backup valves that shut off emergency cooling water to the core and the failure to fix a relief valve that had malfunctioned periodically from October 1978 until the day of the accident.

This relief valve opened to bleed off steam and pressure in the early moments of the accident. In stayed stuck open for almost 11 hours, allowing so much steam to escape that the nuclear core was left without water to keep it covered and cool.

"It is our belief that if this relief valve was working properly the accident would not have been as severe as it was," Stello said. "This was clearly the most serious violation."

For the violation alone, the NRC staff initially proposed a cumulative fine of $63,000 -- $5,000 for each day the relief valve malfunctioned and was not fixed. It settled for $25,000 because of the restrictions of the Atomic Energy Act.

Stello said that the NRC had asked Congress two years ago to amend the Atomic Energy Act to allow it to levy fines of $100,000 for each violation for each day of infraction, without limit.

"We have recognized this problem," Stello said, and have been unsuccessfully seeking legislation to change it."

On Capitol Hill, Sen. Gary Hart (D-Colo.), chairman of the Senate subcommittee on nuclear regulation, said a bill in the Senate would correct this problem by raising the ceiling and eliminating the limit on fines.

"A serious flaw in the current law is the limit a utility may be fined for serious violations," Hart said. "This new provision must be passed as soon as possible to provide a stiffer deterrent."