Nuclear power supporters and critics alike are pressuring the Nuclear Regulatory Commission to say something quickly about the relative safety of nuclear power plants.

The commission's partial repudiation last month of the 1975 Rasmussen Report left industry defenders without their main statistical underpinnings and failed also to satisfy critics who want the entire industry shut down.

The NRC, said Sen. Gary Hart (D-Colo.), "should present the public with a complete, candid and balanced assessment of the risks of nuclear power as soon as it can." Hart, chairman of the Senate subcommittee on nuclear regulation, said he will ask the NRC at its budget hearings tomorrow how it intends to "fill the vacuum" left by its action on the Rasmussen report.

On the other side of the Hill, Rep. Morris K. Udall (D-Ariz.), chairman of the House energy and environment subcommittee which has jurisdiction over the NRC, said he will ask the commission in hearings beginning Feb. 26 if there ought to be another exhaustive study of the entire matter. "Clearly the industry was soothing the public with the Rasmussen report. We have to go back three spaces and start over... to begin to sort out these though questions."

Another report on the scale of the three-year, $4 million Rasmussen study, which involved 60 scienstill scientists and resulted in a foot-thick stack of documents, might not be able to come up with a definitive answer, Udall added.

Rasmussen's principal critic, University of California physicist Harold W. Lewis, agreed with Udall. "Those were honest, competent people who worked very hard," he said. "I think it could have been done better, but not enough better to justify the effort of doing it again."

Lewis, who describes himself as "very pro-nuclear," authored the critique of Rasmussen's study that led to the NRC action.

"I know I put the NRC in a bind, and I find that a little bit ironic," he said. "In a sense they're back to where they were before the Rasmussen study... They and the industry have got to put out a statement that gives the basis for assuring the public of nuclear security."

Rasmussen echoed that sentiment, noting that the public views the NRC action as much more sweeping a rejection than it actually is."The NRC had its own political ax to grind. Maybe they gained some credibility for themselves this way... but they've undermined the credibility of some very reliable methods... Somebody will criticize them now every time they use those methods."

Scott Peters of the Atomic Industrial Forum, the industry trade association, said the NRC should "come up with some guidelines to set everybody's mind at ease." He defended the Rasmussen study as "still a good relative tool, even though flawed" and said some areas that were criticized should be redone so as to be acceptable.

Robert Pollard of the Union of Concerned Scientists, a group critical of nuclear power, said the flaws in the Rasmussen report preclude its use, and that correcting them would not help either,

The main criticism of it, he said, is that its range of probablility for a major accident is too narrow. "But if you broaden it so as to say to the public that the chances [of disaster] range from one in a million to one in 10 million you've conveyed no useful information," Pollard said. "What has to be decided is whether present regulations provide a level of safety high enough to protect the public, and clearly they do not."

A spokesman for the NRC said the barrage of demands for a position statement has been noted there. "They are working on trying to develop a collegial view... but whether they will have one by Monday we just don't know at this point."