The commander of U.S. forces in Iraq today disputed charges that the policy he has helped to implement has failed, and he insisted that the war is "winnable" if the United States shows patience and will.

Army Gen. George W. Casey Jr., who has been nominated to become the next Army chief of staff, made the statements as he came under tough questioning today at his Senate confirmation hearing. Among his sharpest questioners was the top Republican on the Senate Armed Services Committee, John McCain of Arizona, who challenged what he called Casey's "unrealistically rosy" previous assessments and expressed "strong reservations" about his nomination.

Casey, who has served for two-and-a-half years as the top American commander in Iraq, defended his decision to request additional U.S. troops in Baghdad after having previously opposed such a deployment. He also acknowledged that Iraqi Prime Minister Nouri al-Maliki did not request the 21,500 troops that President Bush has decided to send and said Maliki generally opposes increasing the U.S. military presence in his country.

Casey said he asked for two additional U.S. brigades as part of a new plan to secure Baghdad after U.S. and Iraqi military commanders decided they were needed and the Iraqi government gave him the political commitments that were previously lacking. He said the total of five Army brigades that Bush ultimately decided to send to Baghdad would provide "flexibility" to implement the plan.

Bush announced what he described as a new strategy for Iraq last month, authorizing the deployment of 21,500 additional U.S. forces, including 17,500 Army soldiers to Baghdad and 4,000 Marines to the volatile western province of Anbar.

"My general belief is that I did not want to bring one more American soldier into Iraq than was necessary to accomplish the mission," Casey said when asked why he did not request the five brigades himself.

McCain, who has called for additional U.S. forces in Iraq and is considered a potential Republican candidate for president in 2008, questioned whether Casey's judgments made him an appropriate nominee for Army chief of staff.

"While I do not in any way question your honor, your patriotism or your service to our country, I do question some of the decisions and judgments you have made over the past two-and-a-half years as commander of Multi-National Forces in Iraq," McCain said in an opening statement. "During that time, things have gotten markedly and progressively worse, and the situation in Iraq can now best be described as dire and deteriorating. I regret that our window of opportunity to reverse momentum may be closing."

Pointing to the failure of two previous joint U.S.-Iraqi operations to secure Baghdad in the spring and summer of 2006, McCain said, "I'm not certain five additional brigades in Baghdad and one more in Anbar province are sufficient to do the job. I am certain, however, that the job cannot be done with just two additional brigades, as you, General Casey, had advocated."

He challenged Casey to explain "why your assessment of the situation in Iraq has differed so radically from that of most observers and why your predictions of future success have been so unrealistically rosy."

Casey said in his opening statement, "Today, Iraqis are poised to assume responsibility for their own security by the end of 2007, still with some level of support from us."

Before the latest troop-surge plan, he said, he had requested and received additional U.S. troops in Iraq six times -- for military operations and to beef up security for elections.

Casey said the decision to request the two additional brigades came as part of a "continuous assessment process" when he asked the new U.S. division commander for Baghdad to "take a blank piece of paper and tell us what it would take to help the Iraqis restore stability in their capital."

The reason that Iraqis could not do so by themselves is that "the Iraqi security forces are two-and-a-half years into a three-and-a-half-year developmental process," he said, adding, "They are not quite ready to assume security responsibility in Baghdad or Iraq, but they are increasingly ready and willing to take the lead in these security operations with our support."

The general told the committee, "The struggle in Iraq is winnable, but it will . . . take patience and will."

Casey, a 36-year veteran of the Army whose father, a two-star Army general, was killed in Vietnam, took issue with other senior commanders and officials who have described the U.S. policy in Iraq as having failed, and he even said he disagreed with Bush's recent characterization of the situation as headed toward "maybe a slow failure."

"It is not lost on me that the commander in chief wasn't satisfied with what was going on," Casey said in response to questions from the new Democratic chairman of the committee, Sen. Carl M. Levin of Michigan. However, he added, "I actually don't see it as slow failure. I actually see it as slow progress."

Emphasizing the assessment he gave in his opening statement, Casey told the committee, "The situation in Iraq is winnable. It's very winnable. It's hard, though."

Senators of both parties are working on a nonbinding resolution that would express opposition to Bush's troop-increase plan for Iraq while also pledging to protect funding for U.S. forces, including the 130,000 already deployed in the war-ravaged country.

In reply to questions from McCain, Casey said he is in large part responsible for the current U.S. military policy in Iraq and that he does not accept certain downbeat characterizations of it in recent statements by Defense Secretary Robert M. Gates; Marine Gen. Peter Pace, the chairman of the Joint Chiefs of Staff; and Adm. William J. Fallon, the new commander of U.S. forces in the Middle East.

"So you disagree with the secretary of defense, the chairman of the Joint Chiefs of Staff and Admiral Fallon that we had a failed policy?" McCain asked.

"I do, Senator," Casey replied. "I do not believe that the current policy has failed."

Asked about his own previous assessment, given to McCain in December 2004, that "we are on track" to making Iraqi security forces capable of maintaining domestic order and denying Iraq as a safe haven for terrorists by December 2005, Casey said, "That, obviously, has not panned out."

He attributed the reversal of such predictions largely to the rise of sectarian violence after the bombing of a revered Shiite Muslim mosque in Samarra north of Baghdad in February 2006, an event that set off the escalating bloodletting that continues today between Iraq's majority Shiites and minority Sunni Arab Muslims.

Casey said U.S. military policy in Iraq has had two basic goals: reducing the violence by "insurgents and terrorists" and raising the ability of Iraqi security forces to deal with it.

"That is happening in the better part of the country," Casey said. "It is not happening in Baghdad. It is not happening in Anbar. And it is not happening in Diyala province." He said the situation "is definitely deteriorating" in Baghdad and the central part of Iraq, but that "it is not necessarily deteriorating across Iraq." Fourteen of Iraq's 18 provinces have 10 or fewer violent incidents a day, while Baghdad has 30 or 40, he said.

Casey also came under tough questioning from Sen. Lindsey O. Graham (R-S.C.), who challenged the general on the force levels needed to wage a counterinsurgency campaign and disputed his assessment of the portion of Iraq that is peaceful.

"What percentage of the country would it be impossible for an American to walk down the street without being afraid of getting shot at or killed?" Graham asked.

"Probably about half, actually, senator," Casey replied.

In response to questions from Sen. Jack Reed (D-R.I.), Casey said a U.S. surge in Baghdad last year failed to rein in sectarian violence because the Iraqi government did not demonstrate sufficient political will.

"What we did not get when we put those forces in was the political commitment from the Iraqis to target anyone who's breaking the law, not to have any safe havens, not to have political influence on the security forces -- the commitments that Maliki has since made and is delivering on. And that was the difference," Casey said.

"And I was reluctant throughout the fall to ask for additional forces . . . when I knew I didn't have the political commitment of the Iraqis to let us do our jobs," he said, explaining his earlier opposition to increasing U.S. troop levels.

He agreed with Sen. Ben Nelson (D-Neb.) that the latest plan should be reevaluated if the Iraqi government proves unwilling to move against the firebrand Shiite cleric Moqtada al-Sadr and his Mahdi Army militia in the sprawling Shiite slum of Sadr City in eastern Baghdad.

"If we were denied access to Sadr City, I would consider that a significant breach in the commitments that the prime minister has already made, and we would have to have serious discussions with the government," Casey said.

In addition to the violence perpetrated by Sunni insurgents and foreign jihadists, Shiite militias and death squads have killed large numbers of civilians as part of what has been described as an ethnic cleansing campaign in parts of Baghdad and the surrounding area.

"Thousands of Iraqis have died at the hands of death squads, and there needs to be accountability for that, too," Casey said.