A broad Army investigation of military detention facilities in Iraq and Afghanistan has found no pattern of abuse, Army Gen. John P. Abizaid, the top commander of U.S. forces in the region, testified yesterday.

Abizaid disclosed the preliminary finding during a Senate hearing in which he acknowledged that overcrowding and other "systemic problems" at Abu Ghraib prison outside Baghdad may have contributed to the abuse of detainees there. But he rejected a suggestion by Sen. Robert C. Byrd (D-W.Va.) that a "culture of abuse" existed under his command.

"I believe that we have isolated incidents that have taken place," the general said.

Abizaid said he was briefed Tuesday on the Army investigation, which was launched in February and is being led by the Army's inspector general, Lt. Gen. Paul T. Mikolashek. "I specifically asked the IG of the Army, did he believe that there was a pattern of abuse of prisoners in the Central Command area of operation," Abizaid said. "And he looked at both Afghanistan and Iraq, and he said no."

The testimony came during the third of a series of hearings planned by the Senate Armed Services Committee to examine the causes of the prison scandal sparked three weeks ago by the emergence of photographs showing detainees at the Abu Ghraib facility being sexually humiliated and abused in other ways.

Both Abizaid and the senior commander of U.S. forces in Iraq, Army Lt. Gen. Ricardo S. Sanchez, accepted responsibility for the misconduct in opening remarks. But they made clear they were not yet aware of everyone who might be implicated in the scandal because a number of criminal and administrative investigations are underway.

Abizaid promised to hold accountable those eventually found guilty and said some officers and sergeants who so far have received only administrative reprimands for their involvement may yet face criminal charges.

Sanchez strongly defended his decision to put a military intelligence officer in charge of security at the Abu Ghraib facility last November -- a move that Maj. Gen. Antonio M. Taguba sharply criticized in his report on the abuses. Taguba said it violated Army doctrine and helped set the stage for misconduct by making the military guards there subordinate to an intelligence unit responsible for interrogations.

Sanchez said he had not intended to place the guards under the control of the intelligence officer for anything other than actions involving the protection of the prison against attacks by Iraqi insurgents. Command of the prison had become "dysfunctional," he said.

The question of the extent to which traditional lines of command were blurred at the prison between the military police, who guard detainees, and military intelligence personnel, who run interrogations, has also come up in connection with recommendations by Maj. Gen. Geoffrey D. Miller.

At the urging of top Pentagon officials, Miller, who was commander of the detention facility at Guantanamo Bay, Cuba, visited Iraq late last summer to assess interrogation practices. He advised that military police join in "setting the conditions" for interrogations. Taguba's report objected to this, saying it ran counter to Army doctrine and to "the smooth operation of a detention facility."

But Miller, appearing yesterday with Abizaid and Sanchez, disputed Taguba's finding. He said he had urged only "passive intelligence gathering" by the guards on the behavior of detainees, not active participation in the interrogation process.

Miller said Sanchez and other senior officers in Iraq understood the recommendations, although some prison guards implicated in the abuses have said they were following the orders of interrogators to prepare detainees for questioning.

"There must have been a breakdown somewhere," said Sen. John McCain (R-Ariz.), addressing Miller.

"Sir, in my estimation, it's a breakdown in leadership on how that the follow-on actions may have occurred," Miller replied.

Abizaid said that traditional Army doctrine governing how military police and military intelligence personnel relate at detention centers needs to be changed. He said this is one conclusion to emerge from the investigation by the Army's inspector general.

"Our doctrine is not right, it's just not right," Abizaid said. "What do the MPs do, what do the military intelligence guys do, how do they come together in the right way? And this doctrinal issue has got to be fixed if we've ever going to get our intelligence right to fight this war and defeat this enemy."

Reviewing the overall military situation in Iraq, Abizaid predicted that violence could well intensify, even after the planned transfer of limited sovereignty to an interim Iraqi government June 30, because of lingering political uncertainty until elections can be held. He said more U.S. forces might be needed, but reiterated his hope that additional countries would contribute troops. He said Iraq's new security forces should be fully functioning by next April.

During the hearing, committee Chairman John W. Warner (R-Va.) announced that the Pentagon had sent word of the discovery of another disk of photographs depicting abuse by U.S. soldiers. The Pentagon said the disk contains 24 photographs, 13 of which had surfaced previously. The other 11 "may not be original or true photographs" and are being reviewed by criminal investigators, according to a Pentagon letter to Warner.

In Afghanistan, the top U.S. commander, Lt. Gen. David Barno, announced a "top to bottom" assessment of all detention facilities in that country. He said the review would be led by a general who would visit every facility to "ensure internationally accepted standards of handling detainees are being met."

At a Senate Armed Services Committee hearing are, from left, Maj. Gen. Geoffrey D. Miller, Lt. Gen. Ricardo S. Sanchez and Gen. John P. Abizaid.