The commission said it is "aware that there are many questions pertinent to storm restoration efforts" during last week's Hurricane Isabel and the thunderstorms that occurred at the end of August, according to its statement of investigation.

"The commission will conduct a(n) . . . inquiry to review the preparedness and performance of utilities in responding to both major outages," the notice said.

Written reports detailing several items, including the point at which customers "were restored" and "lessons learned" will be required of the companies by Oct. 20. Utility companies must include a comparison of their efforts during Hurricane Isabel with that of Hurricane Floyd in 1999.

The hearings will be held after the commission reviews the reports.

Maryland power companies said they are still working on restoring lights to some of the last customers affected by Isabel. Southern Maryland Electric Cooperative has shared outage numbers with the commission throughout Hurricane Isabel, said Ann Knott, a spokeswoman for the cooperative.

The commission knew that it would be several days before the power was returned, she said.

As of 2 p.m. Wednesday, about 1,100 of the cooperative's customers did not have electricity, Knott said, down from 73,687 customers blacked out. The last of the darkened households should be restored by Thursday, she said.

"Rates will not go up as a result of this storm," Knott said, adding that the utility budgets for storms.

About 55,000 customers of Baltimore Gas and Electric had no electricity as of 6 p.m. Wednesday, with about 21,000 of them in Baltimore County, said Clay Perry, spokesman for BGE's parent company Constellation Energy Group. BGE customers without power in Prince George's County number about 800, and in Montgomery County about 600.

Perry, too, said the additional relief efforts will not affect customer rates.

Pepco said at about 5 p.m. Wednesday, it still has about 33,000 Maryland customers without power, most in Montgomery County, down from more than 500,000 at the height of the storm.

The commission's decision may answer Wednesday's letter from Montgomery County Executive Douglas M. Duncan to Maryland Gov. Robert L. Ehrlich Jr.

Duncan asked Ehrlich to "use the State of Maryland's regulatory authority" to determine the reason that power companies have taken a long time getting power back to customers. Duncan and others have been sharply critical of Pepco's past power restoration performance in other storms.