EDITORIAL In the late 1960s, the Sacramento Municipal Utility District made a terrible decision and began building a nuclear power plant. Rancho Seco started generating power in 1977.

But over the next 10 years, environmental activists put pressure on the elected board that runs SMUD — and in 1989, the public power agency shut down the nuke with 11 years left on its operating license.

Pacific Gas and Electric Co. built Diablo Canyon nuclear plant about the same time — but despite massive public protests, it's still running today. That's a big difference between public power and private utilities — and its one the San Francisco Supervisors need to recognize as they debate power plants in the southeast part of town. Because right now, two big private power companies are setting the agenda for the city's energy policy.

And if they're in control, the environment will be the loser.

Over the past several weeks, Mayor Gavin Newsom has met with representatives of PG&E — which is desperately trying to keep the city out of the retail electric power business — and Mirant Corp., which seems quite happy to keep operating its power plant at the foot of Potrero Hill.

That's unacceptable, and the supervisors need to reject it.

The background on this issue, for those who haven't been paying attention, is fascinating and a bit complex.

For years, residents of the southeast neighborhoods have been trying to shut down the Mirant plant, which runs a natural gas-fired turbine and three diesel-powered auxillary generators. California Independent System Operator (Cal-ISO), which manages the state's electricity grid, has balked at removing the only large-scale generating facility within city limits, saying San Francisco can't bring all of its power in from outside.

Until recently, the San Francisco Public Utilities Commission — with Newsom's blessing — has proposed that the city operate three natural gas turbines, known as peaker plants, that would run only when demand for power is high. Cal-ISO says the peakers would fulfill the in-city reliability requirement, and if they're built, the Mirant Plant would be shuttered.

The peakers (which the city already owns, thanks to a lawsuit settlement) are fossil fuel plants and release air pollution — not as much, the city says, as the Mirant plant, but not zero. So environmental justice activists want to stop the new plants, saying the city can make do with conservation, new renewable energy facilities, and a new power line across the Bay. So far, Cal-ISO disagrees, but the activists are pushing the city to try harder to make the state accept a greener option.

So PG&E and the environmentalists are both trying to stop the supervisors from approving the peakers. PG&E sees them as public power, and is funding a sophisticated lobbying and direct-mail campaign against the city peakers.

That effort has turned Newsom around: as Amanda Witherell reports on page 15, the mayor is apparently prepared to offer a new plan that would scrap the city-owned peakers in favor of retrofitting the diesel units at the Mirant plant. PG&E would bring ...