The FBI (search) is conducting an internal review of its methods of disciplining employees and investigating allegations of wrongdoing, FBI Director Robert Mueller said Friday.

The inquiry, expected to take up to six months, will be led by former Attorney General Griffin Bell and Lee Cowell, a former FBI associate director.

Mueller said the review of the FBI Office of Professional Responsibility (search) comes in response to problems that surfaced in media reports and investigations by the Justice Department's inspector general and Congress.

"FBI employees must trust that allegations of wrongdoing will be thoroughly investigated and that discipline will be appropriate and fair regardless of the assignment or seniority of the employee involved," Mueller said in a statement.

The statement cited "an erosion of trust" in the current FBI process.

The internal review follows a report by Glenn A. Fine, the Justice Department inspector general, concluding that the current head of OPR, Robert Jordan, exercised poor judgment by denying a promotion to a subordinate who claimed on CBS's 60 Minutes that supervisors received lighter punishments than field agents.

Sen. Charles Grassley, R-Iowa (search), has questioned whether Jordan tried to mislead Congress when he told three senators in December that he was unaware of recent cases of light punishment by supervisors.