"In recent days there has been a good deal of discussion of who bears responsibility for the terrible events at Abu Ghraib,"before the Senate Armed Services committee. "As secretary of defense, I am accountable for them and I take full responsibility."
"I feel terrible for what happened to these Iraqi detainees," he said. "For those Iraqis who were mistreated by members of the U.S. armed forces, I offer my deepest apology."
The secretary was interrupted by a group of protesters, who yelled "Fire Rumsfeld!" and "Look at all the abuses in Iraq."
Rumsfeld spoke as some top Democrats were. The New York Times seconded those demands with a Friday editorial headlined "Donald Rumsfeld Should Go."
"If I felt I could not be effective, I'd resign in a minute," Rumsfeld said. CBS News National Security Correspondent David Martin said all bets are off on the secretary's future. President Bush said Thursday he wanted Rumsfeld to remain in the Cabinet.
The abuse controversy erupted last week when CBS News' 60 Minutes II broadcast photographs of apparent abuse. Many showed Iraqi prisoners hooded and naked, stacked in piles or simulating sexual acts.
Rumsfeld's appearance came a day after President Bushto the Iraqi prisoners and their families. Many in Congress have expressed anger that they were not told more about the abuse probe.
Armed Services committee chairman Sen. John Warner, R-Va., said Friday that senators wanted to learn, "Who knew what and when, what did they do about it, and why were members of Congress not promptly and adequately informed?"
Rumsfeld said he "failed to recognize how important it was to elevate a matter of such gravity."
"I wish we had known more sooner and been able to tell you more sooner," he said. "We didn't."
However, Rumsfeld and Joint Chiefs of Staff Chairman Gen. Richard Meyer repeatedly denied that the Pentagon had failed to disclose the abuse probe, referring to two instances where a spokesman for Central Command mentioned the probe.
Rumsfeld warned that other photos and videos may emerge. He said he had only seen the original photos Thursday night.
Sen. Lindsay Graham, R-S.C., referring to the video, said, "The worst is yet to come."
Rumsfeld told senators he is naming several senior former officials to look at the investigations that are already under way – and see if additional probes need to take place.
He also said he was looking for a way to compensate those Iraqis who were abused because, "it's the right thing to do."
The photos have led to criminal charges against six soldiers and administrative findings against seven others. Mr. Bush, Rumsfeld and other officials have insisted the abuse at Abu Ghraib prison in Baghdad were criminal acts by a few soldiers.
But a Red Cross report from earlier this years said the abuse of some Iraqi prisoners was "tantamount to torture" and some abusive practices may have been accepted by the U.S.-led coalition.
Sen. Carl Levin, D-Mich., said the "abusive actions do not appear to be aberrant conduct by individuals" but part of a pattern of intelligence gathering.
Levin said a memo by White House counsel Alberto Gonzales — which said refusing to apply the Geneva Convention to detainees "preserves flexibility" for the military — hinted at a disregard for international law.
Rumsfeld faced questions over whether he had approved a policy of using military police to "enable" the collection of intelligence from detainees. The Army report on the abuse said the guards at Abu Ghraib had been told to "create the conditions" for interrogation.
The defense secretary said he had not seen the policy, but added, "the linkage between the two is desirable if you are concerned with obtaining additional information that can prevent terrorist attacks."
"It is important that there be a linkage, a relationship," Rumsfeld said.
In excerpts of the Red Cross report, printed by the Wall Street Journal, the agency said abuse was not systematic for most prisoners, but it was systematic for those held for intelligence reasons.
Those prisoners "were at high risk of being subjected to a variety of harsh treatments … which in some cases was tantamount to torture, in order to force cooperation with their interrogators," it read.
The report was sent to the United States in February but represented a summary of the information given to U.S. authorities the previous year, Pierre Kraehenbuehl, director of operations for the International Committee of the Red Cross, told a news conference.
He said the abuse of prisoners represented more than isolated acts, and that the problems were not limited to the Abu Ghraib prison
"We were dealing here with a broad pattern, not individual acts. There was a pattern and a system," he said.
Some of the prisoner abuse has been blamed on troops, but private contractors working for the CIA have also come under fire.
Torin Nelson, a former interrogator working for the private firm CACI international, tells Britain's Guardian newspaper that even "cooks and truck drivers" were used to interrogate prisoners, and that many detainees are "innocent of any acts against the coalition".
In a sign of continued problems with the tracking of contracts, Pentagon officials on Thursday acknowledged they have yet to identify which Army entity manages the multimillion-dollar contract for interrogators like the one accused in the Iraq prisoner abuse probe.