The region's long-term plans to generate electricity to serve a growing population and to replace decades-old dirty plants were thrown into disarray this week, when a Los Angeles County Superior Court judge ruled Tuesday that local authorities had failed to do the necessary environmental and health analyses.

The 32-page decision came in response to a lawsuit filed by the Natural Resources Defense Council, Communities for a Better Environment and other groups. In it, Judge Ann I. Jones told the air district it could not sell offsets to the plants without a fuller analysis under California's Environmental Quality Act. In particular, the judge said, the district needed to analyze exactly how many tons of pollutants, including health-damaging soot and planet-heating greenhouse gases, that each proposed plant would emit.

Wallerstein said the district is unlikely to appeal the ruling. "It will be a question of whether we proceed with a new rule, or whether we throw up our hands and say, someone else should figure this out because it is beyond our control."

If the judge's concerns "are beyond our ability to address, then there will be a permanent moratorium on power plant construction in Southern California."

Environmentalists and many industry experts say that much of the region's demand can be met through conservation and renewable energy.