The Alexandria City Council took its first official steps early yesterday morning to evict an unwanted neighbor -- an aging coal-fired power plant that has violated state emissions standards and, according to critics, is contributing to the region's air quality woes.

The council voted to revoke a 1992 agreement that has allowed the 55-year-old Mirant power plant, on the Potomac River shore, to operate outside current zoning regulations and other use permits. The city will also explore the possibility of filing a Clean Air Act lawsuit urging the federal government to impose steep fines on the Atlanta-based energy company.

The move was applauded by environmental activists and neighbors of the plant at the northern end of Old Town.

"It provides a framework for the city to move forward . . . and make sure that until the plant closes, they are good corporate citizens," said City Council member Paul Smedberg (D).

The energy plant and its heap of glittering coal sit on a piece of prime real estate on the banks of the Potomac River. Yet the plant produces power for only Maryland and D.C. customers, not for Virginians. Its presence has long vexed city officials and residents, who fear potential health hazards from the plant's noxious gas emissions and the sooty ash that often dusts their yards and homes. As council member Joyce Woodson (D) put it, "We are looking for them to go away."

Mirant spokesman Steven Arabia said company officials have no plans to close the plant.

"There is a lot of uncertainty surrounding the council's action," Arabia said. "I believe there will be a long, drawn-out process that will ensue now. We're confident that the outcome will be such that we will continue to operate our plant. . . . If we were to close the plant tomorrow, a big portion of Washington, D.C., would be without electricity, and you would not be able to measure any improvement in air quality in Alexandria. For those reasons, we think the action taken last night is not appropriate."

Mirant recently installed new attachments on the plant's smokestacks that will limit nitrogen oxide emissions by at least 15 percent, Arabia said, and additional pollution controls will be added. The company has also agreed to fund a state study on the environmental impact of emissions on surrounding neighborhoods, particularly on nearby high-rise condominiums.

The company is negotiating a new permit with the state's Department of Environmental Quality, after violating its emissions permit last summer and fall. During that time, the state measured 2,129 tons of nitrogen oxide gases emissions, more than 1,100 tons above the limit. Levels are tested in the summer, when warmer air and higher concentrations of noxious gases contribute to ozone trouble.

Arabia said the company believes its permit allows it to swap "clean air credits" from other plants where emission levels are lower than permitted, a practice opposed by state and local officials in Virginia.

Last night, the city also decided to oppose any agreement in the company's ongoing bankruptcy proceedings in a Texas court that would extend the life of the Alexandria plant. Mirant Corp. filed bankruptcy last July and until recently owed the city $1.4 million in taxes -- a debt that the company has now paid off, Arabia and city officials said.

Alexandria resident Elizabeth Chimento, who joined forces with neighborhood activist Poul Hertel to investigate the plant three years ago, said she was happy with the city's decision.

"This will not be a simple process," Chimento said. "It is a very large step forward. . . . For the first time, we have a number of steps in place that will see that the plant will leave. We will watch to make sure as these steps go forward that nothing bogs them down."

Chimento, Hertel and other activists had asked the city to give the plant two years to install the latest pollution control technology, shut down or convert to natural gas. Converting to natural gas could cost between $300 million and $400 million, the city said.

The Alexandria City Council voted to revoke an agreement that has allowed the Mirant plant, on the Potomac River shore, to operate outside some regulations.