Washington (CNN) -- The commander of international and U.S. forces in Afghanistan continues to support the July 2011 drawdown date for troops in Afghanistan, but has not decided on the level of reductions yet, he told senators on Tuesday.
In remarks to the Senate Armed Services Committee, Gen. David Petraeus said the Taliban momentum achieved over the last five years "has been arrested in much of the country." Progress in that effort "is also fragile and reversible," he said.
The top Republican on the committee, Sen. John McCain of Arizona, asked Petraeus to respond to a new poll that showed most Americans say the war in Afghanistan is not worth fighting anymore.
Petraeus said that while he understands the frustration of the American public, he believes it is imperative to continue making progress in Afghanistan so that al Qaeda is not allowed to re-establish sanctuaries in Afghanistan.
"Upfront I can understand the frustration. We have been at this for 10 years," Petraeus said. "We have spent an enormous amount of money. We have sustained very tough losses."
But the general said it is important to remember that Afghanistan is where the plan to attack the United States on September 11, 2001, was made. At the time, the ruling Taliban government harbored the al Qaeda terror network, which launched the attack.
"That's where the initial training of the attackers took place before they went on to Germany and to U.S. flight schools," he said.
Safe havens still exist for insurgent fighters in the Pakistan-Afghanistan border regions. More forces have been positioned to cut off the flow of fighters and explosives from those sanctuaries, Petreus said, but Sen. Carl Levin, a Michigan Democrat, questioned what more could be done.
"Now, Pakistan may be looking the other way in that regard, but I don't think we can look the other way about what they are not doing in those areas," Levin said. "What, if anything more, can we do to persuade the Pakistanis to be the hammer... so that when those forces cross the border, we can be the anvil?"
Under Secretary of Defense for Policy Michele Flournoy, who also testified, said that "extremely candid conversations" were taking place about the U.S. expectations of Pakistan in border areas like North Waziristan.
The concerns are not being ignored, Petraeus said.
"The fact is that the Pakistanis are the first to note that more needs to be done," said Petreaus. "There is, I think, a growing recognition that you cannot allow poisonous snakes to have a nest in your backyard, even if they just bite the neighbor's kids, because sooner or later they're going to turn around and cause problems in your backyard."
Progress is also being made in getting Taliban fighters to walk away from the insurgency, he said. In the recent months, 700 former mid- and lower-level Taliban have officially reintegrated with Afhgan authorities and about 2,000 more are in the process of reintegration, according to Petraeus. A couple thousand more have "informally reconciled," returning home to their villages and laying down their weapons, he estimated.
Among other things, Petraeus highlighted his push to increase the size of the Afghan security forces by an additional 70,000 personnel, bringing the total to as high as 378,000.
Both Defense Secretary Robert Gates and Afghan President Karzai support the move, according to the general.
Petraeus has recommended a minimum Afghanistan force level of 352,000 -- 45,000 more than his original October 2011 goal.
An administration decision on the general's request is expected soon, Flournoy said.
Afghan army and police forces are currently receiving literacy training as part of the U.S. mission, Petraeus noted. Afghanistan's illiteracy rate is higher than 80%.
"If a soldier can't read a serial number off a weapon (or) a policeman can't read a license plate on a car, needless to say that is mission limiting," he told the committee members.
Karzai is expected to announce the first round of districts and provinces that will transition to Afghan force control on March 21.
Petraeus warned the committee that Congress's continuing inability to pass a long-term budget would hamper the U.S. mission in Afghanistan by June.
"That obviously would cause us enormous concern, because the last thing that we want to have to do is to halt our progress in an area that is so important to the ... transition" of responsibility to Afghan government forces, he said.