FBI Director Robert S. Mueller III told Congress yesterday that agents posted abroad have reported instances of possibly improper conduct in prison interrogations overseen by the CIA or U.S. military personnel.

Mueller, testifying before the Senate Judiciary Committee, said FBI agents in Iraq and Afghanistan have been instructed not to participate in interrogations that involve coercive methods and are expected to "report up the chain" if they learn of any possibly illegal conduct by others.

"We have, upon occasion, seen an area where we may disagree with the handling of a particular interview," Mueller said. "Where we have seen that, we have brought it to the attention of the authorities who were responsible for that particular individual."

Mueller provided no specifics about where those incidents occurred, except to say that FBI agents conducting interrogations at Abu Ghraib prison in Baghdad said they did not witness abuse of prisoners there by military police or others.

The CIA's inspector general in recent weeks referred the deaths last year of three prisoners in CIA custody to the Justice Department for investigation and possible prosecution. Two of those prisoners were in Iraq, including one at Abu Ghraib. The third was in custody in Afghanistan.

The deaths occurred during or after interrogations by CIA officers and contractors. As yet, Mueller said, the FBI has not been asked to investigate the deaths.

Sen. Patrick J. Leahy (D-Vt.) pressed Mueller about whether the FBI had refused to participate in CIA interviews of high-level detainees "because of the brutality of the interrogation methods being used." Mueller said the FBI requires its agents to adhere to the same interviewing standards it follows for prisoners held in the United States.

"Senator, it is the FBI's policy to prohibit interrogation by force, threats of force or coercion," Mueller said. "Where we have conducted interviews, we have adhered to that policy."

Referring to the Defense Department and the CIA, Mueller said: "There are standards that have been established by others, legally, that may well be different from the FBI standards. . . . That does not necessarily mean that those standards were unlawful. What I'm saying is that they may not conform to the standard that we use in conducting investigations in the FBI."

Participation by an agent in interrogations that used force or coercion might be used to discredit him in other cases, Mueller said. He also said the FBI generally takes the view that building a rapport with prisoners is more effective in getting information than using fear or force.

Mueller told the panel that alleged prisoner abuse is the responsibility of the Defense Department, and that the FBI is not conducting any prisoner abuse investigations in Iraq, Afghanistan or Guantanamo Bay. The Justice and Defense departments are discussing jurisdictional guidelines for investigating instances of alleged wrongdoing by civilian contractors.

Sen. Charles E. Schumer (D-N.Y.) raised questions yesterday about the U.S. government's hiring in Iraq of two civilian contractors previously accused of overseeing penal facilities where prisoners were allegedly mistreated in this country.

One official, Lane McCotter, resigned in 1997 under pressure as director of the Utah Corrections Department after an inmate died while shackled naked to a restraining chair for 16 hours. Schumer said in a news release issued yesterday that the other, John Armstrong, resigned as head of Connecticut's Corrections Department amid allegations that he tolerated and engaged in sexual harassment of female employees.

Neither is accused of wrongdoing in Iraq.