Anticipating continued growth in the detainee population, U.S. commanders have decided to expand three existing facilities and open a fourth, at a total cost of about $50 million.

The steady influx of prisoners has also required additional U.S. military police officers to guard the detention centers. Commanders had hoped to use the MPs to help train Iraqi police, but management of the detention centers has taken priority.

"We've got a normal capacity and a surge capacity," said Maj. Gen. William H. Brandenburg, who oversees U.S. military detention operations in Iraq. "We're operating at surge capacity."

Last month at Abu Ghraib prison, on the outskirts of Baghdad, the detainee population had grown so large that U.S. authorities decided to stop accepting new arrivals for a few days, Brandenburg said. Instead, detainees were held longer at field camps before being moved to Abu Ghraib. Tents there that normally house 20 inmates now hold 25 to 30, the general said.

The large number of detainees and uncertainty about their fates have become a political issue, with representatives of Iraq's Sunni Arab minority demanding that the inmates be tried quickly or released. More than three-fourths are Sunnis, a fact that U.S. military officers here say reflects the dominant role Sunni groups have played in the insurgency.

Brandenburg said he has argued for allowing the cases to work their way through a process that includes a review board staffed by six Iraqis and three members of the U.S.-led multinational force. As of last week, he said, the board had looked at 10,000 cases and approved the release of about 6,000 people.

But Brandenburg acknowledged that the prisons were filling up faster than cases could be reviewed. "We're still getting more detainees in than we're getting rid of," he said.

A second review board is being established this week to relieve some of the strain on the reviewers, who are facing a heavier workload. Together, the two boards should be able to handle 650 to 700 reviews a week, Brandenburg said. Iraq's Central Criminal Court, created a year ago, has also picked up its pace. It handled 87 trials and 50 pretrial investigative hearings in March.

Various indicators, however, point to a detainee population that is increasingly hard-core and therefore likely to remain locked up. Before January, for instance, the review board had ordered releases in about 60 percent of the cases it considered. In recent months, the figure has dropped to 40 percent.

Similarly, since January, 88 percent of those detained have been rated "high risk" under a six-point system that takes into account the circumstances of capture, severity of the alleged offense and affiliation with known insurgent groups.

Other profiling information provided by Brandenburg shows that 96 percent of those in the detention camps are Iraqis and about 60 percent are either from Baghdad or Anbar provinces -- two areas where much of the insurgency has been concentrated. Only five detainees are female. Nearly three-fourths of the inmate population is between the ages of 20 and 40, and about 60 percent of the detainees have less than a high school education.

Crowded camp conditions and tougher inmates present a combustible mix, confronting U.S. forces with a growing risk of prison violence. Camp Bucca, a sprawling detention facility in the southern Iraqi desert near the Kuwaiti border where the majority of prisoners are held, has experienced two large riots within two months.

As of Friday, Camp Bucca's detainee population had reached 6,370. Another 3,538 are now at Abu Ghraib, the U.S. military's primary interrogation center and the site of highly publicized detainee abuses. Camp Cropper, near the Baghdad airport, houses 114 detainees who are labeled "high value." Another 1,331 suspected insurgents are being held for initial screenings at military brigade and division-level detention facilities, according to military figures.

To cope with the continuing influx, Brandenburg said Camp Bucca, which has eight compounds, is adding two, enough to accommodate about 1,400 additional prisoners. Space for another 800 detainees is being built at Abu Ghraib.

Camp Cropper is also expanding, from a current capacity of about 120 prisoners to 2,000 by the end of this year. U.S. authorities also plan to turn a Russian-built former Iraqi military barracks near the northern city of Sulaymaniyah into a prison for 2,000 inmates and call it Fort Suse.

After briefing Defense Secretary Donald H. Rumsfeld last month on the new construction plans, Brandenburg received word that the Pentagon had approved $12 million to finish the Camp Bucca expansion and $30 million to enlarge Camp Cropper. Another $7.5 million had been authorized earlier to build Fort Suse. The additional capacity at Abu Ghraib will cost less than $1 million, Brandenburg said.

"I think we'll be all right," he said. "But we are very tight."

© 2005 The Washington Post Company