The Abu Ghraib abuse scandal also forced changes in the system, with the military working quickly last summer to try and weed out detainees who obviously did not belong in prison. Many of the ones remaining are more likely to be denied release by review boards, military officials say.

As of this week, the military is holding at least 8,900 detainees in the three major prisons, 1,000 more than in late January. Here in Abu Ghraib, where eight American soldiers were charged last year with abusing detainees, 3,160 people are being kept, well above the 2,500 level considered ideal, said Lt. Col. Barry Johnson, a spokesman for the detainee system. The largest center, Camp Bucca in the south, has at least 5,640 detainees.

One hundred so-called high-value detainees, including Saddam Hussein and his closest aides, are being held at Camp Cropper, near the Baghdad airport.

"We're very close to capacity now," Colonel Johnson said.

The surging numbers of prisoners pose important challenges for the military. The Abu Ghraib scandal revealed that the military was using poorly trained interrogators even as more detainees were swept into prison in the fall of 2003.

The military must hire enough effective interrogators and military intelligence officers to process detainees quickly, said Bruce Hoffman, an analyst at the RAND Corporation who has worked in Iraq with American policy makers. Otherwise, innocent people will languish in the prisons, a fertile recruiting ground for the insurgents, and could take up arms when they are freed.

Throughout the war, the American military has struggled to construct a detainee system that can handle a widespread and sophisticated insurgency, but never before has the system had to grapple with so many detainees.

On a recent morning here, military policemen marched 50 handcuffed men off a convoy that had just arrived from Tikrit, Mr. Hussein's hometown. Old and young, the detainees wore thin shirts or robes. Some were barefoot.

A sign on a concrete blast wall read, "No Parking: Detainee Drop Off Zone." Guards stood watch in towers along walls laced with razor wire. The detainees huddled quietly on the ground outside a squat building where they would be processed. Soon they would be asked to put on orange jumpsuits.

At the main gate, minibuses brought in family members for a visit, many of them solemn young children and unsmiling women in black robes.

Some military policemen complain of understaffing and of being overworked. One policeman based in Tikrit said field artillery soldiers were being assigned to policing duties.

While the military has turned to such soldiers to perform police work, Colonel Johnson said they had been trained for the job.

A senior American commander said there was little danger of "serious overcrowding" in the system. At Abu Ghraib, 15 miles west of Baghdad, the military has erected additional quarters for detainees and has increased troop levels. To increase the number of soldiers on guard duty, commanders have sometimes had to make unpopular decisions like temporarily shutting down family visits, Colonel Johnson said.

Since last May, when news reports first emerged of the grim conditions at Abu Ghraib, formerly Mr. Hussein's main torture center, the military has opened new compounds at the prison that "are much better situated for both the detainees and for custody and control," Colonel Johnson said.

The military is considering moving the detainees from Abu Ghraib to a more secure location around Baghdad International Airport, the same area where Camp Cropper is situated. The new center would hold about 2,500 people at most, though ideally the inmate population would stay under 2,000, Colonel Johnson said.
Last summer, after the Abu Ghraib scandal became public, President Bush promised to raze the prison, but a military judge later ordered that it be preserved as a crime scene.

In the south, the Americans are working to expand Camp Bucca to accommodate a total of 6,000 detainees by the end of March, officials say.

It was an incident at Camp Bucca on Jan. 31 that most recently exposed the potential hazards of the detainee system: Four detainees were killed and six wounded when guards fired shots to quell a well-organized uprising. The guards had replaced their nonlethal weapons with lethal ones after realizing that detainees had armed themselves with slingshots that could hurl stones for long distances. Since then, the military has bought guns that fire "plasticized projectiles" at a greater range, Colonel Johnson said.

Commanders say the uprising at Camp Bucca was not a result of overcrowding, but of skillful organization on the part of imprisoned insurgents. The detainee system has become more efficient at quickly screening people who do not pose a threat, so the prison population is likely more dangerous than before, officials say.

"We're getting more of the right people in," Colonel Johnson said. "So there is certainly an element of the hard-core population."

A very small percentage of detainees are released shortly after being brought to Abu Ghraib, where all detainees bound for the three major centers are first processed. About 1,300 have been turned over to the Iraqi criminal courts to prosecute. Most, though, wait an average of three to four months - and sometimes six months, the limit set by the Geneva Conventions in cases of prisoners of war - before their files go to a review board, Colonel Johnson said.

Mr. Hoffman, the RAND analyst, said using the six-month limit as a standard was ridiculous, since many of the detainees were not soldiers and should have had their cases reviewed much faster.

"Many of them are innocent civilians swept up," he said. "Prisons are the main incubators for terrorists and insurgents. So you've got to have good intelligence in the prisons to process the prisoners quickly and efficiently."

Investigations into the Abu Ghraib scandal last May found that there had been a shortage of professional interrogators to handle the detainee flow, and so units inside Abu Ghraib had turned to untrained military policemen and policewomen to help with interrogations. Colonel Johnson declined to give the number of interrogators now working in the system's main intelligence gathering center inside Abu Ghraib. But he said "there is sufficient personnel to accomplish" the center's mission.

Outside of the three major prisons, about 1,300 detainees are being held at the division or brigade level around the country. Of those, about a third - people deemed to be security threats or of high intelligence value - will eventually be brought to Abu Ghraib for processing and sent onward to a major center. Convoys bring an average of 20 to 100 detainees a day to the prison.

On the recent run from Tikrit, some members of the Third Platoon of the 42nd Military Police Company, a National Guard unit, complained of how the company was overworked and its resources stretched too thin.

Of the company's three platoons, one was guarding the 42nd Infantry Division's prison in Tikrit, another was assigned to protect the division's generals, and the third transported detainees.

In the three weeks after company arrived in Iraq on Feb. 1, the Third Platoon made 25 convoy runs all across the hostile Sunni Triangle, with a dozen of those to Abu Ghraib.

"We've got just enough people to do this" said Specialist Chris DiModica, 23, the driver of the command Humvee. "If anyone gets sick, that's it."