A former top official in the Prince George's County Department of Environmental Resources was indicted yesterday on charges that he demanded a $250,000 bribe from a company seeking to do business with the county, state prosecutors said.

Robert L. Isom, 69, of Upper Marlboro, the department's former deputy director, is charged with conspiring with others -- including at least one county employee -- in a bribery scheme that ran from Sept. 29, 2004, to Feb. 11, 2005. The indictment did not name the other county employee.

The contract involved work to upgrade security at county buildings, three government officials with direct knowledge of the investigation have told The Washington Post.

Reached at home yesterday, Isom said he was disappointed about the indictment.

"Definitely. But that's part of life. You make mistakes, and I made a mistake," he said. "I'll just put it like this: I made a mistake in having two friends and trying to just do what I felt was right at the time.''

He would not elaborate on that comment and referred further questions to his lawyer and longtime friend, Charles Maddox, who declined to comment.

State Prosecutor Robert A. Rohrbaugh said "rules of ethics" prohibited him from commenting on the investigation.

Sources familiar with the investigation have told The Post that the subcontractor was supposed to pay installments of several thousand dollars.

The sources said Isom and Robert L. Thomas, then-deputy director of the Office of Central Services, allegedly took at least one payment while the firm was cooperating with state investigators. The Office of Central Services handles county contracts and purchases as well as the management of buildings and vehicles.

Thomas has not been charged. He could not be reached yesterday.

The company, which has not been identified, contacted investigators after Isom allegedly asked for money in exchange for awarding a contract, the sources said.

Isom was deputy director of the Department of Environmental Resources from July 2004 to May 2005.

The three sources told The Post that on May 24, the state prosecutor's office seized records and computer equipment from Isom and Thomas. Isom was fired after county officials received affidavits from the prosecutor's office outlining the information compiled by investigators.

Jim Keary, a spokesman for the county, told The Post that Thomas quit several weeks before the records and computers were seized.

Before working for the county, Isom was the deputy assistant inspector general for inspections and evaluations at the D.C. Office of the Inspector General.

He also has run for the Prince George's County Council.