The Army general in charge of U.S. forces in the Middle East said today that the abuse of Iraqi detainees at a prison near Baghdad was part of "systemic problems" at the facility and that he accepted responsibility for them. But he denied the existence of a broader "culture of abuse" in U.S. military detentions.

Gen. John P. Abizaid, commander of the U.S. Central Command, vowed to "follow the trail of evidence wherever it leads" and to hold accountable anyone responsible for the mistreatment.

Appearing with two other generals and a colonel before the Senate Armed Services Committee, which is investigating the prison abuse scandal, Abizaid warned the nation to brace for even more violence in Iraq from insurgents and foreign terrorists in the months ahead, and he allowed that more U.S. troops might be needed "because the enemy has a vote."

In the course of a wide-ranging hearing that lasted more than three hours, Sen. John Warner (R-Va.), the committee chairman, said legislators should also brace for more prison abuse photos. He remarked that he had just been notified by the Defense Department that "another disc of pictures has been located." He said arrangements would be made for senators to view them.

Questioned on the situation in Iraq aside from the reported mistreatment at Abu Ghraib prison west of Baghdad, Abizaid said that Abu Musab Zarqawi, a Jordanian terrorist with links to the al Qaeda network, appears to be able to move around Iraq and to "strike at will." Zarqawi claims to have ordered numerous suicide bombings that have killed hundreds of people in Iraq, and U.S. authorities blame him for the car-bomb assassination Monday of Izzedin Salim, the acting president of the Iraqi Governing Council. Zarqawi is also believed to be the masked man who recently beheaded an American civilian, Nicholas Berg, in a video that was posted on the Internet.

Abizaid said U.S. authorities have reason to believe that Zarqawi recently was in neighboring Jordan, where he was allegedly involved in a plot that would have killed thousands of people if it had not been foiled by Jordanian forces.

"We should not kid ourselves about the violent times ahead," Abizaid told the committee. He said U.S. forces face "a patient and despicable enemy" in Iraq that will cost the United States "more blood and more treasure." And he cautioned that the worst violence may come between the time the U.S. occupation authority hands over political power to Iraqis on June 30 and the first national elections, which are scheduled for early next year.

"They must make it fail now," Abizaid said of the insurgents' approach to the transition to democratic self-government in Iraq. "They're pulling out everything that they can to make it fail."

U.S. forces are winning "tactical battle after tactical battle" in Iraq, Abizaid said, but he acknowledged that the war has a huge nonmilitary dimension.

"While we cannot be defeated militarily, we aren't going to win this thing militarily alone," he said. "It's really one of the hardest things this nation has ever undertaken."

In response to senators' questions, Abizaid said he was "pretty comfortable" with the number of combat troops and weapons systems in Iraq. What makes him uncomfortable, he said, is that "there are certain types of troops we don't have enough of," notably military police, military intelligence personnel and civil affairs officers. This is because "they're not in the force structure," he said.

"I'm also not comfortable that there's enough international troops on the battlefield," Abizaid said. "Maybe I miscalculated" the number of the troops that would be needed to occupy Iraq, he conceded. "But we adjusted . . . and we continue to adjust."

The size of the force in the future "depends on the enemy," he said. "It's possible we might need more forces." He expressed hope that, with a new U.N. resolution, more international forces might be dispatched to Iraq.

Appearing with Abizaid, Lt. Gen. Ricardo S. Sanchez, the commander of U.S. forces in Iraq, said that in addition to court martial proceedings already initiated against seven military personnel over the Abu Ghraib scandal, "there may very well be more prosecutions" as a result of several ongoing investigations.

Shortly before the hearing, Spec. Jeremy Sivits pleaded guilty in a court martial in Iraq and was sentenced to one year in prison, to be followed by discharge from the Army for bad conduct. He had confessed to pushing a prisoner into a pile of naked Iraqis who were photographed on the prison floor at Abu Ghraib.

Abizaid said the military has investigated about 75 cases of detainee abuse in Iraq and Afghanistan, as well as some cases of prisoner deaths.

"Abuse has happened in Afghanistan, it's happened in Iraq, it's happened at various places," Abizaid said. But he said the inspector general of the Army, in preliminary findings of an investigation, has not found a pattern of abuse of prisoners under Central Command control.

Contrary to reported findings of the International Committee of the Red Cross, Abizaid said, "I don't believe that a culture of abuse existed in my command. . . . I believe that we have isolated incidents that have taken place."

On the other hand, he said there appeared to be "systemic problems" at Abu Ghraib, possibly caused in part by a shortage of military police to guard detainees. Another systemic problem, he said, lay in getting intelligence collected from detainees to the commanders who could use the information in their operations against insurgents.

And he said the Abu Ghraib scandal has exposed a problem in Army procedures on how to deal with reports such as those produced by the Red Cross.

"This system is broken," Abizaid said. "We've got to fix it."

Sanchez disputed another Army general's account of an order he issued on Nov. 19, 2003, to place Abu Ghraib under the tactical control of a military intelligence brigade commander. Sanchez said the order had to do with force protection because the prison complex was regularly taking fire from insurgents. He said the order was not intended to remove the responsibilities of the military police brigade commander whose soldiers guarded prisoners at Abu Ghraib.

Maj. Gen. Geoffrey D. Miller, the new deputy commander for detainee operations in Iraq and former commander of the detention facility at Guantanamo Bay, Cuba, testified that a mission he led to Iraq last year did not encourage any of the abuses. He said a report he produced recommending that military police help "set the conditions" for successful interrogations referred to "passive intelligence gathering" by military police, such as observing detainees to see who they talked with. He said military police were encouraged to pass such information along to interrogators, but were barred from participating in the interrogations.

Abizaid acknowledged confusion about the roles of military police and intelligence personnel, saying it was part of a broader problem.

"Our doctrine is not right," he 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're ever going to get our intelligence right to fight this war and beat this enemy."