Mirant Corp. plans to propose that its Alexandria power plant be allowed to reopen on a limited basis while the company seeks solutions to the environmental problems that resulted in the plant's shutdown last month, documents filed with federal regulators show.

Under a tentative plan Mirant outlined last week, the Potomac River plant would operate at a level "significantly reduced from full capacity," one that does not violate national air quality standards. At the same time, Mirant would continue studying long-term remedies such as burning cleaner coal or increasing the height of the plant's smokestacks so that pollutants disperse better.

The plan must pass muster with the Virginia Department of Environmental Quality (DEQ), which has ordered Mirant to take immediate steps to reduce pollution. DEQ spokesman Bill Hayden said the department has not yet seen a proposal from Mirant but "will take a look at what they do propose. The main thing we're looking for is, if they are continuing to operate, it must be in a way that does not violate air-quality standards.''

Federal regulators, meanwhile, are also evaluating a petition, filed by the D.C. Public Service Commission, that asks them to order the plant's reopening. In documents that Mirant filed last week with the Federal Energy Regulatory Commission, the company revealed that it is likely to propose the partial reopening.

Amid the blitz of regulatory activity, it remains unclear when the plant, which was providing electricity to homes in the District and Maryland, but not Virginia, might reopen even temporarily. And Mirant acknowledges that a full-scale resumption of operations could be more than a year away.

Mirant decided on Aug. 24 to shut down the plant in response to the order from Virginia officials to cut potentially harmful pollution from the coal-fired facility. The directive by the Department of Environmental Quality came after it reviewed the results of an analysis that showed that some pollutants found in the plant's vicinity are sometimes considerably higher than national standards allow.

Neighbors of Mirant have complained for years about what they believe to be high levels of contaminants emanating from the plant. But the 56-year-old plant was supplying enough electricity to serve about 400,000 homes in the District and Maryland, and officials with Pepco and the D.C. Public Service Commission have described it as a vital link in the Washington power grid.

Without the plant's generating capacity, if other transmission circuits failed there could be a blackout "in much of the District of Columbia" affecting all electricity customers in Georgetown, Foggy Bottom and major portions of downtown Washington, Pepco wrote in a filing last week with the Federal Energy Regulatory Commission.

"Numerous federal facilities will lose power, including those crucial to the security, safety and welfare of the whole country, such as the FBI, the Justice Department, the State Department,'' wrote Pepco, which distributes electricity in the region.

Officials at Pepco and the D.C. Public Service Commission acknowledged last week that the plant's shutdown has not yet affected the power supplied to residents. "So far, we've gotten by because we haven't had the kind of conditions that could lead to sudden blackouts, like equipment failures, and we've had relatively mild weather,'' said D.C. public service Commissioner Richard E. Morgan.

"But it still could happen,'' he added.

Pepco said it doesn't plan to let things get to that point. The company announced that it plans to work with the D.C. commission to accelerate construction of new transmission facilities that would ensure reliable electrical power even without the Mirant plant.

"Given Mirant's recent decisions, we believe action is necessary to satisfy Pepco's obligation to provide reliable service to our customers,'' said Dennis Wraase, president and chief executive officer of Pepco Holdings Inc. Constructing transmission facilities is expected to take about 18 months.

Pepco said that for now it supports the D.C. Public Service Commission petition asking federal regulators to order the plant's reopening. Bryan Lee, a spokesman for the Federal Energy Regulatory Commission, would not say when the commission will make a decision.

Mirant remains determined to reopen the plant. "We're confident that we're going to find a solution that will allow us to get our plant back into service and restore the level of electric reliability that we've come to expect,'' Mirant spokesman Steve Arabia said.

The report that precipitated the shutdown looked at worst-case scenarios involving pollution, weather and operational capacity. Researchers found that under certain conditions, the levels of sulfur dioxide, nitrogen dioxide and particles in the vicinity of the Mirant plant are higher than national ambient air-quality standards allow.

As a result, state officials directed Mirant to take immediate steps to reduce pollution from the plant. Mirant decided to shut the plant down until it could find a way to meet air quality standards.

Atlanta-based Mirant, which filed for bankruptcy in 2003, operates four plants in the Washington area, including three in Maryland: in Montgomery, Prince George's and Charles counties.

Poul Hertel, a neighbor who has helped to lead the fight against the plant, said he is skeptical about Mirant's plan to reopen on a limited basis. He said the problem of polluted downwash from the plant's smokestacks could worsen.

"Downwash is not proportional to how much they are producing, it's more proportional to the speed and velocity of the emissions,'' Hertel said. "Just because they are operating at lowered capacity doesn't mean the issue is by any way, shape or form resolved.''