One reason Pennsylvania Gov. Richard Thornburgh never ordered an evacuation of nearby homes in the wake of the nuclear accident at Three Mile Island is that one man in the state government told him not to.

That was the message from four state officials and one county official who testified before the Kemeny Commission investigating the acdcident. They all agreed that on Friday, March 30, two days after the accident began, most state and federal officials were telling Thornburgh to begin evacuating residents of towns and villages within five miles of Three Mile Island.

But Thomas M. Gerusky, director of the state Bureau of Radiation Protection, after hearing that the federal Nuclear Regulatory Commission and the state civil defense director had recommended evacuation, drove to the State House, marched into Thornburgh's office and advised him not to evacuate anybody.

"I drove there because I couldn't get through to him by telephone," Gerusky told the Kemeny Commission. "And when I arrived there I told the governor there was no evacuation needed."

In the hour before Gerusky appeared at the State House on Friday morning, state Civil Defense Director Oran K. Henderson spoke by telephone to Lt. Gov. William K. Scranton III and recommended that Thornburgh order an evacuation out to a five-mile radius of the Three Mile Island plant, an area that took in 36,000 people.

"I had just spoken to the NRC, which was recommending a 10-mile evacuation," Henderson testified."They had conveyed to me the seriousness of the situation."

Henderson and Gerusky both testified that there was mass confusion about an evacuation plan on Friday, with the state leaning to a five-mile evacuation and the NRC to a 10- or even 20-mile evacuation. Gerusky said the confusion was typified during a phone conversation he had with the NRC's Harold (Doc) Collins.

"The conversation was a wild one," Gerusky testified. Collins "said it wasn't his recommendation (to evacuate), that he was just following orders, and then he hung up. I couldn't get Civil Defense on the phone and I couldn't get the governor's office on the phone so there was only one thing left to do. We went to the governor's office and told him not to evacuate."

The confusiion began just after 8.30 a.m. on Friday, when plant operators at Three Mile Island spoke by phone with the Civil Defense Office and told officials there had been a release of radiation serious enough to trigger evacuation.

"They said there was a release of 1,- 200 millirems [1.2 rems an amount above the minimum level recommended for evacuation] 600 feet above the stack," Henderson testified, "and that we ought to be prepared for an evacuation downwind.

"Two of my people were talking to plant operators," Henderson went on, "and the first one off the phone looked at me and said, 'This guy's going ape.'"

"Just after that, Collins called from NRC Headquarters in Bethesda and asked Henderson: "Do you have the latest?" When Henderson said he did, Collins said: "We're recommending you initiate a 10-mile evacuation," Henderson said he told Collins: "We have no plans for a 10-mile evacuation, but we will consider a five-mile plan." That's when Henderson recommended the five-mile evacuation to Thornburgh.

Gerusky testified that he'd been told that Friday morning's radiation release was "planned but uncontrolled," that the first 1,200-millirem burst would be the strongest and that later release would taper down to much less than that.

"By the time we got to the governor's office," Gerusky told the Kemeny Commission, "NRC Chairman [Joseph] Hendrie had called and told Thornburgh they had made a mistake and they apologized and said there was no need for an evacuation,"

Later to testify yesterday was Collins, who said that NRC engineers had calculated the worst-case accident would result in a 1,200 millirem release "off the site" of the plant. Just after they had done so, the NRC got a phone call that said there had been a 1,200 millirem release.

"The air changed to one of severe aprehension," Collins said. "We did not realize at the time that the 1,200 millirems was right over the stack and not off site a half mile away. Communications were not very good."