The Supreme Court yesterday upheld the government's controversial decision to license nuclear power plants without weighing the risks of disposing of the radioactive waste generated by each plant.

The unanimous ruling, an important victory for the nuclear power industry, removes a cloud over the status of at least 100 plants that have already been licensed, according to Nuclear Regulatory Commission officials.

Those licenses would have had to be reconsidered had the justices not struck down an earlier lower court decision.

The ruling also means that environmental groups and others cannot raise the waste disposal issue to tip the balance against licenses for future plants, as they had hoped.

The court said the NRC has already determined that the waste, largely spent fuel, can be safely stored hundreds of feet underground in salt formations and thus presents no significant environmental impact. The agency need not reconsider its finding every time a new license is sought, Justice Sandra Day O'Connor wrote for the court.

Courts should be especially deferential to agency decisions made "at the frontiers of science," she said.

"We're very disappointed," said Barbara A. Finamore, attorney for the Natural Resources Defense Council, which spearheaded a decade-long fight against the NRC licensing policy.

"The Supreme Court appears to be more confident than we are that the government will be able to safely dispose of the nuclear waste from our nation's reactors," she said.

It is an "extremely important" triumph for the industry, said Linda L. Hodge, lawyer for the Atomic Industrial Forum, the industry trade organization.

It was the third major nuclear power ruling by the Supreme Court this year in the long-running court battle between the industry and its opponents.

The industry suffered a serious setback April 20 when the court, interpreting a different law than the one at issue yesterday, ruled that the states could halt plant construction pending resolution of the waste disposal issue. The court said that Congress did not intend to completely preempt state regulation of nuclear power.

Groups opposed to nuclear power lost one on April 19, however, when the justices said the potential "psychological stress" associated with operation of a plant was legally irrelevant to licensing decisions.

That decision, like yesterday's, was based on the National Environmental Policy Act, which mandates an "environmental impact statement" before proceeding with major projects, such as construction and operation of nuclear power plants.

The Natural Resources Defense Council, supported by 15 states, told the court that the impact statement for each plant should include a judgment about the safety hazards of waste disposal, and vigorously disputed the NRC's "zero-release assumption" that the radiation will not leak into the environment.

The U.S. Court of Appeals in Washington, in a decision written by Senior Judge David L. Bazelon, ruled against the NRC. The court reversed Bazelon yesterday by an 8-to-0 vote. Justice Lewis F. Powell Jr. took no part in the case.

The impact of the decision, with its caution to courts to defer to regulatory agencies, could extend to regulatory decisions well beyond those involving nuclear power.

The method used by the NRC--called "generic rule-making"--to avoid individualized environmental impact determinations has now been approved by the Supreme Court, encouraging other agencies to use the same technique where possible in the future.