(CNN) - A Senate committee hearing on Gen. David Petraeus, picked by President Barack Obama to be the top U.S. commander in Afghanistan, was marked Tuesday by bickering over Obama's plan to begin withdrawing troops in July 2011.
Senate Armed Services Committee Chairman Carl Levin, D-Michigan, stressed the date's importance, saying it "imparts a sense of urgency to Afghan leaders" and is an important method of "spurring action." When the date was announced, Levin said, there was a surge in recruits for the Afghan army.
But Arizona Sen. John McCain, the ranking Republican on the committee, said Obama should make clear that any U.S. withdrawal from Afghanistan will be determined "solely by conditions on the ground."
Potential allies are less willing to back the U.S. mission in Afghanistan because they believe American troops will leave in July 2011, he said, and announcing a date to begin troop withdrawals is making the war "harder" and "longer." The "facts on the ground" suggest more time is needed, McCain said.
The "same people" who were "defeatist" about the war in Iraq now have a similar attitude toward the Afghan war, McCain said.
The deadline has been a source of contention between Obama and Republican critics. Petraeus, however, told lawmakers he supports and agrees with it.
"I saw (the establishment of the date) most importantly as the message of urgency to accompany the message of enormous (increased U.S.) commitment," he said.
The general pointed to Obama's recent reminder that "July 2011 will mark the beginning of a process, not the date when the U.S. heads for the exits and turns out the lights." He quoted Obama as saying, "We'll need to provide assistance to Afghanistan for a long time to come."
"Moreover, as President (Hamid) Karzai has recognized, and as a number of allied leaders noted at the recent G-20 summit, it is going to be a number of years before Afghan forces can truly handle the security tasks in Afghanistan on their own," Petraeus said.
"The commitment to Afghanistan is necessarily, therefore, an enduring one, and neither the Taliban nor our Afghan and Pakistani partners should doubt that."
The general offered praise for his predecessor, Gen. Stanley McChrystal, who resigned last week as the U.S. commander in Afghanistan after he and his staff were quoted in a Rolling Stone magazine article criticizing and mocking key administration officials.
"Gen. McChrystal has devoted his entire professional life to the defense of this nation, and he and his family have made enormous personal sacrifices," Petraeus said. "I can attest, for example, that the success of the surge in Iraq would not have been possible without Gen. McChrystal's exceptional leadership of our special mission unit forces there.
"Most importantly, of course, he has made enormous contributions in leading the coalition endeavor in Afghanistan over the past year," Petraeus said. "We now see some areas of progress amidst the tough fight ongoing in Afghanistan. Considerable credit for that must go to Stan McChrystal."
And Petraeus strongly defended the U.S. mission in Afghanistan, telling senators "we should never forget that the 9/11 attacks were planned in southern Afghanistan and that the initial training of the attackers was carried out in camps in Afghanistan."
"Our task in Afghanistan is clear," he said. "We cannot allow al Qaeda or other transnational extremist elements to once again establish sanctuaries from which they can launch attacks on our homeland or on our allies."
Conditions in Afghanistan have drawn increased scrutiny recently. More than two-thirds of the additional troops Obama ordered into Afghanistan in December are there now, but the momentum of the Taliban has not slowed, and U.S. troop deaths are mounting. In addition, the war - the longest in U.S. history - faces challenges that include problems with Karzai's government and drug trafficking.
Petraeus said Tuesday he was "part of the process that helped formulate the president's strategy for Afghanistan," and he supports and agrees with Obama's policy. "During its development, I offered my forthright military advice and I have assured the president that I will do the same as we conduct assessments over the course of the months ahead."
He said he is aware of concerns raised by some troops on the ground "about the application of our rules of engagement and the tactical directive. They should know that I will look very hard at this issue."
"The (current Afghan) campaign plan is sound," he said, but he told lawmakers he will see whether "tweaks" are needed. "By and large, I think this is more about executing now than it is about redesign," he said.
Until this year, he said, the Taliban and its affiliates had "steadily been expanding the areas they control and influence."
But this year, American troops have made progress in several locations, he said. "The initial main effort has been in the Central Helmand River Valley. And Afghan, U.S. and U.K. forces have expanded security there, though, predictably, the enemy has fought back as we have taken away (extremists') sanctuaries. ... Nothing has been easy in those operations."
Petraeus also highlighted the U.S. troop buildup in Kandahar province, "an area of considerable importance to the Taliban."
Petraeus acknowledged, however, that military operations in Afghanistan's Marjah province are not going as well "as the most optimistic (initial) predictions." While progress is being made, he said, it has been harder and slower than anticipated.
McCain cited the pace of the Marjah operations as one of the reasons for his opposition to the July 2011 withdrawal date. Sen. James Inhofe, R-Oklahoma, also criticized the deadline, telling Petraeus he thinks the Taliban believes the United States will "cut and run."
Petraeus said that "recent months in Afghanistan have seen tough fighting and tough casualties."
But "this was expected," he said. "The going inevitably gets tougher before it gets easier when a counterinsurgency operation tries to reverse insurgent momentum.
"My sense is that the tough fighting will continue. Indeed, it may get more intense in the next few months. As we take away the enemy's safe havens and reduce the enemy's freedom of action, the insurgents will fight back."
The general said one of his goals in Afghanistan is to help ensure the Afghan people know who "has been killing the vast majority" of innocent civilians in their country. "There's no love lost for the Taliban" among civilians, he said.
Petraeus hearkened back to his previous experience heading the U.S. military surge in Iraq. The terror group al Qaeda in Iraq was hurt by successful U.S. efforts to give them an "extremist" label, he asserted.
He urged members of Congress to pass an Afghanistan war supplemental funding bill now under consideration.
"Enabling further such progress ... and successfully implementing the president's strategy will require that our work in Afghanistan is fully resourced," he told committee members.
Defense Secretary Robert Gates is ready to make a recommendation to Obama on a new commander to replace Petraeus at U.S. Central Command, a senior Pentagon official told CNN Tuesday. An announcement is expected shortly after Petraeus is confirmed by the Senate, the official said Tuesday.