A senior U.S. Army general who investigated the abusive treatment of prisoners in Iraq said yesterday that the CIA may have avoided registering up to 100 detainees in U.S. military facilities, a number far higher than the eight cases that Army officials had previously cited.

The disclosure by Gen. Paul J. Kern at a Senate hearing stunned lawmakers, who grew more aggravated as they heard Kern and another general involved in the probe describe their own unsuccessful efforts to obtain documents from the CIA about the unregistered prisoners, known as "ghost detainees." The Geneva Conventions generally require countries to register prisoners so their treatment can be monitored by the International Committee of the Red Cross.

"It's totally unacceptable that documents that are requested from the CIA have not been forthcoming," said Sen. Carl M. Levin (D-Mich.), the ranking minority member of the Senate Armed Services Committee.

"The situation with the CIA and ghost soldiers is beginning to look like a bad movie," said Sen. John McCain (R-Ariz.). "This needs to be cleared up really badly."

The CIA's handling of detainees emerged as a concern in two reports released last month -- the Army's investigation of abuses at the Abu Ghraib prison outside Baghdad, and a broader independent review of Pentagon detention operations led by former defense secretary James R. Schlesinger. Both reports urged further review of CIA activities, with Army investigators concluding that CIA actions contributed to an atmosphere of "confusion and uncertainty" at Abu Ghraib over the treatment of prisoners.

The CIA has said it is conducting its own probe of the agency's detention and interrogation practices in Iraq, citing this as the reason it declined to share information with Army authorities. CIA spokesman Mark Mansfield said yesterday that the agency has asked the Pentagon to provide it with any allegations of CIA abuse.

One intelligence official with knowledge of the investigation said CIA headquarters approved the hiding of only several detainees. The official said field operatives then, evidently acting on their own, began to delay registering other prisoners. Record-keeping on these individuals was virtually nonexistent.

"There were lax procedures for them, and we just don't know much about them," the official said.

Another intelligence official said one reason for not registering some detainees would be to keep their capture secret from other prisoners, thereby impeding the coordination of cover stories that hampers interrogations.

The unresolved question of CIA accountability was one of a number of concerns singled out yesterday by lawmakers in the House as well as the Senate at hearings examining who was to blame for the prison abuse scandal. Republican and Democratic members expressed frustration over the missing pieces to the puzzle of how the mistreatment was allowed to happen on the wider scale now documented.

"Why would all these people not follow Army regulations, not report violations to the Geneva Conventions, wait months to inform commanders of vital information?" Sen. Jack Reed (D-R.I.) asked the Army generals. "I don't think you've reached that, to me, basic question of what went on out there."

So far, only lower-ranking service members have been charged in the abuses. Both the Army and Schlesinger panel reports implicated military and civilian authorities up the chain of command for failure to ensure sufficient numbers of troops, issue clear policies or otherwise exercise proper leadership. But both reports also sought to spare higher-level authorities from prosecution, arguing that they were not directly responsible for the abuses.

Rep. Joel Hefley (R-Colo.) said he is concerned about a "disparity" that would cause senior officers who knew about or condoned abuses to avoid criminal trials.

"Much responsibility for misconduct ultimately lies with senior civilian Pentagon leaders who created a postwar operational environment that facilitated these abuses," said Rep. Ike Skelton (D-Mo.), ranking minority member on the House Armed Services Committee. "Congress must now demand accountability."

Kern, whose team found no one above the rank of brigade commander culpable, agreed under Senate questioning to reassess those findings and look at whether Lt. Gen. Ricardo S. Sanchez, then senior U.S. commander in Iraq, and some of his staff should face prosecution.

Kern called the ghost detainee issue "one of the more troubling pieces of" the Army's probe. Asked to estimate the total number of cases, Kern said it could be "in the dozens to perhaps up to 100."

Maj. Gen. George R. Fay, a lead investigator who appeared with Kern, put the number "somewhere in the area of maybe two dozen or so, maybe more." But both men said the lack of documentation from the CIA makes any estimate difficult.

Fay said his initial requests to the CIA for information went unanswered. After meeting in Washington earlier this summer with the CIA's inspector general, Fay was told that the agency was doing its own investigation.

Kern said that the CIA had obtained permission to bring detainees to the Abu Ghraib facility from then-Brig. Gen. Barbara Fast, the senior U.S. intelligence officer in Iraq. But she expected that CIA operatives would abide by U.S. military rules -- something that did not happen, Kern acknowledged.

The Army's investigation determined that no memorandums of understanding existed between the CIA and Sanchez's staff over the handling of detainees.

Levin urged that the Senate committee make its own "direct request" to the CIA for details about the ghost detainees. Sen. John W. Warner (R-Va.), the committee chairman, said he has been talking with the head of the Select Committee on Intelligence about how to proceed. He held open the possibility that the Armed Services Committee would hold its own hearing on the subject.

Schlesinger told the House Armed Services Committee yesterday that his panel also received little cooperation from the CIA. When pressed, Schlesinger said that relations between the CIA and the Pentagon demand "better definition." He suggested that lawmakers turn their questions to the intelligence community.

Defense Secretary Donald H. Rumsfeld has acknowledged his own involvement in one ghost detainee case. He disclosed in June that he had agreed last November to a CIA request to hold a man suspected of being a senior Iraqi terrorist at a detention center in Baghdad without registering him. Levin said one question he would like to explore is whether this decision contributed to the hiding of other prisoners.

Staff writer Dana Priest contributed to this report.