Nuclear power experts who clashed on nearly everything else agreed reluctantly yesterday that the public may never get a definitive yes-no answer on nuclear power safety.

Pressed by Rep. Morris K. Udall (D-Ariz.) to advise his subcommittee on energy and environment how to respond to public worry on the issue, the experts fudged. It depends on what you mean by safe, they said.

"So many discussions about nuclear power seem to have as a premise, spoken or unspoken, that the objective is zero risk," said Harold W. Lewis, physicist of the University of California at Santa Barbara. That, he said, to general agreement, is "intellectual sloth," since all energy sources present some risks. "There is risk, and our job is to understand and limit it," he said.

Udall called the hearing to reevaluate nuclear safety questions in the wake of the partial repudiation by the Nuclear Regulatory Commission last month of the Rasmussen Report, a reassuring 1975 study of nuclear safety by MIT physicist Norman C. Rasmussen. The NRC branded the Rasmussen report unreliable in its calculation of the probability of a nuclear power plant disaster, an action that rocked the industry.

Still, all sides agreed yesterday that the report probably should not be redone.

"The basic result -- that reactor accident risks are small compared to other societal risks -- remains valid," Rasmussen said. It would be better to concentrate on making existing plants safer and designing them better in accordance with problems noted by his chief critic, Lewis, than to redo the report, Rasmussen added.

Members of the NRC said the report did not need redoing because it had never been the chief support for safety regulation or the issuance of licenses to power plants.

Industry critics responded that the Rasmussen report had been "massively important" in justifying licensing decisions that should not have been taken. "The prime motive... was to develop a technical defense of the industry view," said Daniel F. Ford, head of the Massachusetts-based Union of Concerned Scientists.

Papers obtained by the USC under the Freedom of Information Act, he said, revealed that the Rasmussen report had been written "in close collaboration with the nuclear industry" which had been "a religion in search of a bible."

Ford called for establishment of an outside permanent review board to keep an eye on NRC decisions.

Rep. Jonathan B. Bingham (D-N.Y.) said "the convenience of the (electric power) utilities" and their costs may have had an undue influence on NRC safety decisions.