It was incorrectly reported in yesterday's Washington Post that deuterium is a radioactive isotope of hydrogen.

The new Department of Energy is in the midst of a struggle over whether the science and technology of laser fusion should be kept under military control or be given civilian leadership.

For the time being at least, the $120 million-a-year program to produce fusion power for laster light will be kept secret and will continue to come under the Energy Department's assistance secretary for defense programs. But the decision to keep laser fusion under military control was made only after a long debate inside the fledgling department.

"There was a decision made at one level to take laser fusion out from under the military," one agency source said. "But this decision was reversed at a higher level."

Acting Assistant Secretary Robert D. Thorne told the Senate Energy Committee yesterday of the decision to maintain military controls over the laser fusion program, which has been under way for more than five years. Thorne said the decision was made "because of the classified nature of its day-to-day operations."

The Energy Department inherited laser fusion from the new-defunct Energy Research and Development Administration, which itself inherited the program from the Atomic Energy Commission. The old AEC and its two successor agencies are responsible for nuclear weapons testing and development.

There had been a strong push by environmentalists and by private industry to remove laser fusion from military controls. As recently as last week Thorne was showing an organizational chart around Capitol Hill that had the program under civilian leadership.

"That chart was withdrawn," an Energy Department source said. "It could happen that eventually laser fusion might get civilian leadership, but it won't come right away."

Laser fusion research and development received $116 million from Congress this fiscal year, with most of the money to be spent at the nation's nuclear weapons laboratories at Sandia and Los Alamos, N.M., and at Livermore, Calif. KMS in Ann Arbor, Mich. Exxon Corp., and the University of Rochester also do some laser fusion research.

Fusion by laser involves striking pellets of deutenum and tritium gas with laser light so powerful and intense it melts the pellets and ignites the gas in an instant, producing temperatures of hundreds of thousdands of degrees. The secrets involved in the process surround the making of the pellets, not the laser that ignites the pellets.

"The way these pellets are made comes right out of nuclear weapons technology," one source said. "It involves secrets that are crucial to the way hydrogen bombs are exploded."

THe pellets are tiny balloons filled with what scientists call DT gas, a mixture of deuterium and tritium. Both radioactive isotopes of hydroden they are key ingredients in [WORD ILLEGIBLE] clear warheads.

Sources said that one reason the Energy Department was pressured to go laser fusion under civilian control was the feeling that the work bond would move faster. Said to be at least 25 years away from practical use fusion power could provide a clear and limitless source of electricity.