In a letter to leaders of the Department of Water and Power, Hahn wrote that the city wouldn't need the extra electricity that would be generated by expanding the Intermountain Power Plant, a giant coal-powered generator that is shared by the DWP and other utilities.

The DWP gets about one-third of its electricity from the Delta, Utah, plant. Environmentalists attacked the city's plans to invest in its expansion, saying ratepayer dollars shouldn't be spent on high-pollution power sources.

"Basically, we're not going to need a third coal plant in Utah," said Deputy Mayor Doane Liu. "We don't need a large surplus of electricity at this point."

The DWP has spent about $1.7 million on the proposed expansion of the Intermountain Power Plant so far, said the city utility's acting general manager, Enrique Martinez. The expansion is scheduled for completion in 2009.

The DWP has no assurance of a refund of the $1.7 million, which was spent for legal and engineering fees.

The DWP and its partners, including Intermountain Power Agency and municipal power systems, had included a sunset clause in their study agreement, Martinez said. Come October, the partners have to decide whether to go forward with the expansion or drop the project.

The existing two coal-fired units at Intermountain will continue to operate and provide the city with 9.2 million kilowatt-hours a year. Martinez said the city's stake in the expansion was small and the electricity supply should not suffer.

Environmentalists have long criticized the DWP's reliance on coal for electricity. Earlier this year, they joined Hahn and City Council members Tony Cardenas and Alex Padilla in calling on the DWP to draw 20 percent of its power from cleaner, renewable sources by 2017.

Environmentalists hailed Hahn's order for the DWP to withdraw from the Utah plant expansion.

"It clearly states that the future for the DWP is in renewables, the past is in coal," said Martin Schlageter, energy program director for the Coalition for Clean Air. "We're just glad the decision has been made now before (spending) more money on bad air."

The Utah plant expansion could increase carbon dioxide emissions by 20 percent, further polluting the air basin over the Grand Canyon, officials said.

"We always knew it was a concern with coal and some of the other issues that go along with it," Martinez said.

Still, DWP considered the 950 megawatt expansion a good long- term investment, providing an additional stable source of electricity compared to natural gas-fired plants that can suffer occasional spikes in fuel cost.

By James Nash and Kerry Cavanaugh