WASHINGTON -- CIA Director Michael V. Hayden has mounted a highly unusual challenge to the agency's chief watchdog, ordering an internal investigation of an inspector general who has issued a series of scathing reports sharply critical of top CIA officials, according to government officials familiar with the matter.

The move has prompted concerns that Hayden is seeking to rein in an inspector general who has used the office to bring harsh scrutiny of CIA figures -- from former Director George J. Tenet to undercover operatives running secret overseas prison sites.

The probe is focused on the conduct of CIA Inspector General John L. Helgerson and his office. Officials said it is aimed in particular at evaluating whether his office was fair and impartial in its scrutiny of the agency's terrorist detention and interrogation programs. But officials said the probe also spans other subjects and has expanded since it began several months ago.

U.S. intelligence officials who are concerned about the inquiry said it is unprecedented and could threaten the independence of the inspector general position. The probe "could at least lead to appearances he's trying to interfere with the IG, or intimidate the IG, or get the IG to back off," said a U.S. official familiar with the probe.

Frederick P. Hitz, who was the CIA's inspector general from 1990 to 1998, said the move would be perceived as an effort by Hayden "to call off the dogs."

"What it would lead to is an undercutting of the inspector general's authority and his ability to investigate allegations of wrongdoing," Hitz said. "The rank and file will become aware of it and it will undercut the inspector general's ability to get the truth from them."

But other officials described the probe as a chance to turn the tables on an inspector general who has been accused by some of his targets of treating career officers unfairly and letting personal biases undermine his objectivity.

"There is across-the-board distrust with the IG function and disrespect for Helgerson, who many believe has a personal agenda on issues," said a former high-ranking CIA official who, like others interviewed, spoke on condition of anonymity because of the classified nature of the inspector general's work. Helgerson, the former official said, "always went in with a presumption of guilt."

Helgerson oversees a large staff of investigators whose activities include everything from detailed examinations of highly classified programs to routine audits of mundane agency functions. He has been inspector general at the CIA since 2002.

The CIA probe comes at a time when the powers of inspectors general in agencies throughout the federal government are under renewed debate. This month, the Bush administration threatened to veto a House bill that would strengthen the independence of inspectors general by giving them seven-year terms and permit the White House to fire them only for cause.

Hayden, an Air Force general who became CIA director last year, has not been involved in any publicly known clashes with Helgerson. But Hayden has been a staunch defender of the Bush administration's counterterrorism programs, and has lamented what he describes as a tendency by outside observers and critics to second-guess the activities of the nation's intelligence agencies.

In response to questions about the unusual arrangement, CIA spokesman George Little said that Hayden "firmly believes that the work of the Office of Inspector General is critical to the entire agency, and, since taking the helm at CIA, he has accepted the vast majority of its findings." However, Hayden's goal is "help the office do even better," Little said.

The CIA's review is being led by Robert Deitz, an attorney with long-standing ties to Hayden who was brought in to be a senior counselor to the director. Deitz, who was general counsel at the National Security Agency when Hayden was director there in the 1990s, has assembled a small team of investigators to conduct the probe.

Little, the CIA spokesman, said Deitz came to the post with "an absolute belief in the value of an independent, rigorous Office of Inspector General."

The inquiry has been driven in large part by senior operations officers who have complained to Hayden that they were unfairly criticized by Helgerson in classified reviews of the CIA's secret prisons programs.

The probe is set up to examine "how those people were treated, how the investigations were conducted," said an official familiar with the probe.

The official declined to discuss the conclusions of those IG investigations, which are classified, but said that "the people who are upset didn't think they were glowing reviews."

Among the issues being explored are whether agency officers were given adequate opportunity to defend their actions, and whether the inspector general's conclusions accurately represented their roles.

Officials declined to provide names of the CIA officers behind the complaint. One former official said, "We're talking about undercover people at mid- to senior-grade ranks."

The CIA created a network of secret overseas prisons shortly after the Sept. 11 attacks, and has faced severe international criticism for employing harsh interrogation tactics as well as a program known as "extraordinary rendition," in which prisoners have been transferred to countries known to use torture.

To date, officials said, the probe has largely involved gathering information and statements from CIA officers who came under scrutiny in Helgerson's review.

But officials expressed concern that the probe will also involve reviewing the inspector general's files. Such a step could have a dramatic, chilling effect, officials said, making agency employees reluctant to cooperate with future investigations for fear that their involvement and the information they provide would be exposed.

The focus on the prison program represents an expansion of a probe that began several months ago into the relationship between Helgerson's office and that of the CIA general counsel.

Officials said that Hayden was concerned about friction between the two offices, and tapped Dietz to explore the matter. The nature of the friction was unclear, but involved complaints that Helgerson had overstepped his role by offering legal opinions on agency programs.

Greg Miller writes for the Los Angeles Times.