The public should have confidence in the quality of nuclear power regulation rather than seeking to rely on some mathematical estimate of nuclear safety, Nuclear Regulatory Commission Chairman Joseph M. Hendrie said yesterday.

The regulatory process, Hendrie said, is "prudent and conservative... not a system that depends on determining what the probability of an accident is." The NRC last month partly rejected a 1975 study, the Rasmussen report, which gave nuclear disaster a very low probability, but the NRC "did not thereby take a new view of reactor safety," Hendrie said.

Only "relatively few" and "insignificant" changes in current NRC procedures for licensing and regulating nuclear plants will be needed, Hendrie added.

That view, echoed by other commissioners who testified with Hendrie before the Senate environment and public works subcommittee, brought sharp disagreement from the panel's chairman, Sen. Gary Hart (D-Colo.).

"Professional assurances about the low degree of risk were very important to the public perception of that risk," he said. The public view, he said, "may be fundamentally altered" by the change in the NRC evaluation of the Rasmussen report, since the report was "very, very central" to the feeling that nuclear power is safe.

"People are now saying, 'What can we rely on?" Hart continued. "If you are saying those numbers are not reliable it will reverberate back through the society."'

Commissioner Victor Gilinsky acknowledged that "to the extent that people relied on those numbers, we'd have to say they didn't have those numbers to rely on any more."

He added that it might cause the commission to pay more attention to the safety of operating reactors, as opposed to that of those under construction, since some past decisions to allow continued operation presumably were based on the discredited numbers. A staff study is due in the next two or three weeks on the extent of that use, Hendrie said.

The commissioners for the first time admitted publicly to some division of opinion over their reaction to the new view of the Rasmussen study.

Commissioner Peter Bradford said he had objected to the phrase in Hendrie's remarks that "effective quality assurance programs" had guaranteed the public safety to this point.

"That word 'effective' may promise too much and I would not have used it," Bradford said. "Not all past decisions, not all licensing decisions, did in fact provide adequate protection to the health and safety of the public." He added, however, that he agrees on the fundamental safety of nuclear power.

Asked by Sen. Pete V. Domenici (R.N.M.) why the commission had taken three months to issue its statement on the Rasmussen report, Hendrie replied, "In a nutshell, we argued from September until mid-January over the precise language."

On a related matter, Hendrie said the commission still did not know how an employe of a Wilmington, N.C., nuclear power plant managed to get out of the facility with two cans containing 145 1bs. of low-level enriched uranium powder. The theft had been discovered last week in routine counting of the cans, he said, admitting that loss of that much powder by weight was "down in the noise area" of inventory figures and probably would not have been noticed.

The safety issues were raised as part of Hart's hearing on the NRC's request for $374 million in the fiscal 1980 budget, an increase of 13 percent over this year's level.