A House subcommittee investigating the March 28 nuclear accident at Three Mile Island today was given the operators' version of what happened and it often conflicted sharply with what the House members had been told by the Nuclear Regulatory Commission.

Operations Supervisor Jim Floyd told the 14 surprised members of the subcommittee on energy and the environment that federal inspectors knew the plant's fuel core was damaged two days before they said they were told. He added that operators could not have known a relief valve was stuck open, allowing water to spew out, uncovering the core, because of a red light went off in the middle of their control panel telling them the valve was closed.

"This light was supposed to go out when the valve closed, the operator saw that happen and he assumed the valve was close," Floyd told the subcommittee in the control room of the stricken Three Mile Island plant. "But in fact, even though this light went off telling the operator the valve had closed, the valve stayed open for several hours, draining all the hot water out of the system," Floyd said.

Floyd preceded that revelation with the disclosure that a hydrogen explosion in the containment building the NRC has said it was not informed of for two days had been witnessed on control room equipment by two NRC inspectors. Floyd said the inspectors were standing on either side of the Three Mile Island operator when the tracing pen on the containment pressure gauge leaped up and stayed there for almost two hours.

"We thought they were cognizant of what was happening," Floyd said. "But apparently they didn't comprehend what they saw."

Floyd said it would have been difficult for the two NRC inspectors to ignore the "spike" in pressure indicating an explosion because it triggered an automatic fire control spray inside the containment that had to be turned off manually by the Three Mile Island operator at whose side the inspectors stood.

"The NRC people," Floyd said, "were right there the whole time."

NRC Commissioner Victor Gilinsky, who accompanied the touring Congress members, said it was news to him that NRC inspectors may have known about the hydrogen explosion two days before he and his four fellow commissioners were told. The fact that hydrogen exploded inside the containment told the NRC that the fuel core was damaged, since the hydrogen could only have come from the breakup of water by fuel bundles hot enough to break open themselves.

"This is the first I've heard that we may have observed it when it [the explosion] happened," Gilinsky said. "Gilinsky said. "It will be a subject of review."

Floyd today told how two operators, one foreman and a shift supervision-all licensed by the NRC-scrambled frantically in the early hours of March 28 to cope with an accident that came so fast they hardly had time to think. He said the instruments on the control panel often gave the four men late and misleading information. He said the chain of events that triggered the accident rang "anywhere from 50 to 100 alarms" in the first two minutes.

"I felt a kind of sympathy for the operators after today's visit to the control room," Rep. Morris K. Udall (D-Ariz.), chairman of the subcommittee, said in an interview on the flight back to Washington, D.C., from Three Mile Island. "It's 4 o'clock in the morning, lights and bells are going off and you've got a few minutes to make decisions that may involve a big disaster. I saw the situation through their eyes a little better today."

The operations supervisor admitted that a set of auxiallary feedwater pumps were locked out of service in violation of NRC rules at the time of the accident and stayed locked out for eight minutes before an operator noticed it. But Floyd blamed a yellow tag blocking the operator's view of two red lights on the control panel that, had he seen them, would have alerted him right away to the lock-out.

"The operator was standing too close to the control panel and missed the lights the first time but the light indicator was covered by the tag," Floyd said. "It wasn't until eight minutes passed that he stepped back and noticed that both valves were closed and he was able to open them up to get water into the system."

Later, Udall said, "I've spent four years trying to get a handle on nuclear power and there in the control room they're explaining how minutes may have been lost of damage done because some 10-for-a-penny tag was covering a light. Here's a whole system worth $1 billion and some poor operator's under all this pressure who can't find a light that's covered up by some tag hung on a switch."

Before the congressmen heard Floyd, they were told the blocked valves that kept out auxillary cooling water for eight minutes was the fault of someone in the plant. The president of the company that owns Three Mile Island said the valves were closed for inspection 42 hours befor-the accident and were never reopened as they should have been.

"Something fell through, the procedure reopening the train was not done," said Herman Diekamp, president of General Public Utilities Corp. "The only conclusion I can draw is that a supervisor who initialed that checklist failed to follow it through."

"Who did it?" Dieckamp was asked. "We have the name of that person," he responded. "His response to our questions about it was 'I thought I completed that.'"

But Floyd stole the show with his explanations inside the control room, whose cramped control panel was a far cry from the modern and easy-to-follow panel most of the House members expected to find.

Floyd showed them a control panel that printed out backup temperature and pressure readings inside the reactor that were anywhere from 20 minutes to an hour behind real measurements. He showed the House panel another backup temperature gauge that was located on the back of the regular control panel and not readily visible.

The Three Mile Island supervisor said that operators were confused by instruments that indicated coolant temperatures of 285 degrees when they were closer to 500 degrees. He said they were also confused by pressures that fell to 1,200 pounds, then 1,000 pounds and then went up to 1,200 pounds again, but he never absolved the operators from blame.

"I think they concentrated too much on one thing as the sources of their problems," Floyd said. "Once a man gets on a track, it's hard for him to step back and become objective. These operators were victims of that. It's called tunnel vision, I guess." CAPTION: Picture 1, Reps. James Weaver (D-Ore.), Morris Udall (D-Ariz.) and Austin Murphy (D-Pa.) visit Three Mile Island control room where they were briefed by plant operators. AP; Picture 2, Aerial view of the Three Mile Island nuclear power plant which was visited by a House energy subcommittee. House Interior Committee