"It's a serious issue when you tell us to walk away from that," she said.

The cities' decision came amid pressure from politicians and environmentalists.

Gov. Arnold Schwarzeneg- ger signed legislation in September imposing a first-in-the-nation emissions cap on utilities, refineries and manufacturing plants, with a goal of cutting greenhouse gases to 1990 levels by 2020. Burning coal releases carbon dioxide, among the biggest of the heat-trapping greenhouse gases.

Burbank's city council initially planned to beat the clock and renew its contract with Intermountain until 2044 — the cities won't be able to renew those contracts after the new greenhouse gas law takes effect Jan. 1 — but it changed course.

Sen. Dianne Feinstein, D-Calif., wrote to an umbrella group for the cities last week saying she was "shocked and dismayed" by Burbank's initial decision.

Searle said the company was looking at ways to modernize its plants to bring them into compliance with California's new greenhouse-gas legislation. Its current customers are mostly in Utah and Southern California.

The company is exploring burning biomass such as switchgrass, wheat straw and cornstalks instead of coal, or possible burial of carbon dioxide, he said.

Intermountain also extended its renewal offer for any sort of power from the plants until 2023. Utility officials hope state regulators will let them renew the contracts if greenhouse gases are reduced.

Greenhouse gas levels in the atmosphere reached a record high in 2005, with the concentration of carbon dioxide alone rising by about 0.5 percent, the World Meteorological Organization reported this month. The U.N. agency described the greenhouse gases are the major drivers behind global warming and climate change.

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