"Nuclear reactors are not safe," Dr. Edward H. Teller, the 71-year-old physicist, told a House committee yesterday, "but they are incomparably safer than anything else we might have to produce electric energy."

Teller's theme was echoed by a panel of nuclear scientists that included three Noble laureates.

Although the hearing by the House Committee on Science and Technology was scheduled long before the March 28 accident of Pennsylvania's Three Mile Island nuclear power plant, that event and Sunday's massive rally here against atomic power became the focus of the session.

The lessons the scientists said should be learned from the Pennsylvania accident were almost directly contrary to those recited on the Capitol grounds Sunday by nuclear power opponents.

"Coal plants put out more radioactivity than Three Mile Island did," said Dr. Eugene Wigner, a 76-year-old Princeton theoretical physicist and 1963 Nobel laureate.

"Why not take the people out of Boulder, Colo., [Where the background radiation is almost double that of Washington]?" Wigner asked at one point. "Why not forbid mining and burning coal?

"If we have to take risks with nuclear or other types of power, the risks are much less with nuclear," he said.

Three Mile Island "may have proved meltdowns may never happen," according to Dr. Karl Cohen of Stanford University, once chief scientist for the General Electric Co., who helped in the development of nuclear reactors.

The "major outcome," he said, "may be the psychic damage done by panic mongerers."

The "principal risk is the risk to the operators," he said. "Utilities will take the rap. The public was quite well protected."

At least two committee members lashed out at statements by the scientists.

Rep. Richard Ottinger (D-N.Y) at one point launched into a long list of criticisms despite what he termed his "tremendous respect for the scientific genius at the table."

"Must we count our blessings that Three Mile Island didn't kill anybody? Before we call a call a halt to nuclear reactors to we have to kill tens of thousands?" he asked.

The Ottinger sortie drew a cold response.

He charged that "some of you" took part in the Manhattan Project which developed and built the atomic bombs "that caused thousands of deaths," linking that role to their current views on nuclear power.

Cohen responded that was a "broad indictment" and that he did not "believe anyone had to apologize" for working for the government during a world war.

Rep. Jerome Ambro (D-N.Y.) asked if scientists agreed there would be far-reaching health effects if one of the 71 nuclear plants currently operating had an explosion."

Dr. Hans Bethe, 72, of Cornell University responded that there "can never be a nuclear explosion."

Ambro asked about the well-publicized danger of a hydrogen explosion at Three Mile Island.

Bethe responded that there was "no oxygen" in the containment area "and therefore no explosion was possible."

At the time of the accident, however, Nuclear Regulatory Commission officials believed some oxygen could be in the containment vessel and that an explosion was possible.

On the topic of solar power, Bethe, also a Nobel laureate, said it "will remain about four times the price of fission (nuclear) power" and for that reason he does not see it as economically practical for larger cities. "For a small community, about 100 houses, that is a different matter," he added.

Another target of the panel was President Carter's programs to cut down on nuclear proliferation.

Several panel members criticized the attempt to halt breeder reactors-those that create more pluonium than they use.

They also argued against administration efforts to prevent other countries from having reprocessing plants-facilities that take spent reactor fuel, extract plutonium and other fission products and return enriched uranium for reuse.

"Limiting reprocessing is a terrible mistake," Wigner said.

"The U.S. has a choice of what kind of fuel it can use," Bethe said of decisions the nation can make on both nuclear and non nuclear energy sources. "But most other industrial countries don't have a choice." CAPTION: Picture, Testifying at the House Committee on Science and Technology hearing on the future of nuclear energy were scientists, from left, Hans A. Bethe and Karl Cohen, Robert Hofstadter of Stanford University, and Behram Kursunoglu of the Center for Theoretical Studies of the University of Miami in Florida.