"We've been at this for more than 10 years," Petraeus said. "We've spent a lot of money and there have been difficult life-changing wounds...I was at Walter Reed yesterday...."
"I think it's important to remember why we are there. That's where 9/11 began -- that's where the plan was made," he said. "We do see al Qaeda looking for sanctuaries all the time... ."
A Taliban-controlled Afghanistan would attract a significant amount of al Qaeda members, Petraues predicted.
Although the American people have heard that argument before, Petraeus said the U.S. only started to get its "input" right in the war in the last two years since focus shifted back to Afghanistan from Iraq.
"I do believe we can build on that progress," he said. "As difficult as that may be, I believe it's imperative that al Qaeda not be allowed to establish sanctuaries in Afghanistan."
Nearly two-thirds of Americans now say the Afghan war has not been worth fighting according to a Washington Post-ABC News poll, a record high that comes as the war, already the longest in American history, approaches its eleventh year.
In the poll, 64% of all Americans said the Afghan war hasn't been worth fighting -- including 49% who feel that way strongly -- both record highs. Further, only 31% said the war had been worth fighting, a record low.
At the hearing, Sen. John McCain (R-AZ), urged patience and warned of an expected uptick in violent Spring clashes.
"We are turning around the war in Afghanistan, but as Petraeus says, this progress remains fragile and reversible," McCain said.
McCain also said the recent poll numbers remind him of the low level of support for the Iraq war in the fall of 2007 when the majority of the Senate wanted an immediate pullout before the "surge" and how so many had expected the strategy to fail.
"I have a bit of a feeling of de ja vu," McCain said.
Despite the slow and fragile progress, Petraeus said he still expects to comply with President Obama's deadline for a July draw-down in forces but said he still has not decided how much of a reduction in troops he would recommend ahead of that date.
"I think it is logical to talk about getting the job done...and beginning transition and a responsible reduction in forces at a pace determined by conditions on the ground," Petraeus said.
In terms of cooperation from Pakistan in the fight against the Taliban and al Qeada, Petraeus said he sees progress.
"There is a growing recognition [in Pakistan]," Petraeus said, "that you cannot have poisonous snakes in your backyard even if they just bite the neighbor's kids because at some point, they will turn around and bite you."
MichÃ¨le A. Flournoy, Undersecretary of Defense for Policy, said U.S. forces are having "extremely candid conversations about what we would like our Pakistani partners to do" in terms of pressuring al Qaeda senior leadership in the border regions.