Washington (CNN) -- Conservative and liberal lawmakers Wednesday sharply criticized President Obama's plan to start a U.S. troop withdrawal from Afghanistan in July 2011.
Most Republicans backed the president's decision to send more troops. They claimed, however, he was playing politics by setting an "arbitrary" withdrawal deadline while insisting that any transfer of responsibility to the Afghan government ultimately will be based on conditions in that country.
They also argued he inadvertently strengthened the hand of Taliban and al Qaeda extremists by allowing them to know when a U.S. departure from the war-torn country would begin.
Several members of the Democratic caucus, on the other hand, expressed unease with the president's decision to send thousands of additional troops over the next several months. They questioned whether the war is winnable.
Obama's blueprint faced questions Wednesday as Secretary of State Hillary Clinton, Defense Secretary Robert Gates and Adm. Mike Mullen, chairman of the Joint Chiefs of Staff, appeared before two key committees.
"I disagree with the president's decision to personally relay to our enemies when they can regroup and when they can retake Afghan territory," said Rep. Connie Mack, R-Florida and a member of the House Foreign Affairs Committee.
"I simply cannot understand and cannot agree with this approach," Mack said, adding that Obama's decision "emboldens our enemies [and] allows them to prepare and plan."
Announcing a firm date for starting an American withdrawal while also saying such a withdrawal depends on conditions in Afghanistan "are two incompatible statements," said Sen. John McCain of Arizona, the Senate Armed Services Committee's ranking Republican.
"You either have a winning strategy ... and then once it's succeeded, then we withdraw or, as the president said, we will have a date [for] beginning withdrawal in July 2011. Which is it? It's got to be one or the other. It's got to be the appropriate conditions, or it's got to be an arbitrary date. You can't have both."
Gates noted the administration will conduct "a thorough review" of the Afghan strategy in December 2010.
"If it appears that the strategy's not working, and that we are not going to be able to transition in 2011, then we will take a hard look at the strategy itself," Gates said.
"The president always has the freedom to adjust his decisions," Gates said, adding that Obama has made "a clear statement of his strong intent."
In a televised speech Tuesday night from the U.S. Military Academy, Obama announced that he will send an additional 30,000 U.S. troops to Afghanistan while setting a goal of starting to bring forces home by summer 2011.
The new deployment, estimated to cost $30 billion a year, will bring the number of U.S. service members in Afghanistan to roughly 100,000. NATO allies are expected to add at least another 5,000 troops to the 40,000-plus they already have contributed to the U.S.-led mission.
The new strategy is designed to eliminate al Qaeda in Afghanistan and help the Afghan government defeat the Taliban insurgency, while bolstering Pakistan's anti-terrorism efforts.
"The success of this operation depends on will and resolve," argued Sen. Lindsey Graham, R-South Carolina. "I just don't want the July 2011 statement to be seen by our enemy [to mean] that we have somehow locked ourselves into leaving."
Clinton said she does "not believe we have locked ourselves into leaving, but what we have done ... is to signal very clearly to all audiences that the United States is not interested in occupying Afghanistan."
The Afghan people, Mullen noted, ultimately have to win the war by themselves. The U.S. military buildup is "about partnering and mentoring just as much if not more than it is about fighting."
The administration is not "going to throw these guys into the swimming pool and then walk away," Gates said in reference to Afghan military and civilian authorities.
But it's important to establish a timeline in part to "build a fire under them, frankly, to get them to do the kind of recruitment, retention, training and so on, for their forces that allow us to make this transition," Gates said.
Gates and Mullen noted the Afghan military is slated to increase from 134,000 troops in December 2010 to 170,000 by July 2011.
They also indicated the initial transfers of responsibility will take place in areas marked by less fighting.
The administration's "timeline is clear," Mullen said. The flexibility "is in where we transition [and] where we turn over responsibility."
White House Press Secretary Robert Gibbs dismissed GOP claims that the Taliban and al Qaeda could wait out the surge and return after the start of a U.S. withdrawal in 2011.
"I consider [it] to be a highly illogical argument [that] these people are going to recede into the woods, they're going to give up their land, they're going to give up what they control," he said.
"If that's the case, great. That would be the best outcome, because American forces would then take that real estate. ... If [the extremists] want to come back in July 2011 and start this process over again, they'll meet a far larger Afghan national security force to take them on."
Some Democrats, however, questioned the necessity of continuing the conflict.
"We've been there eight years now and we're still talking about turning it around," said Rep. Bill Delahunt, D-Massachusetts. "Is [another] 18 months going to be sufficient?"
The top Democrat on the House committee that controls war spending told reporters he is skeptical despite Obama's speech and will try to attach benchmarks to a war funding bill he expects Congress to consider next year.
"The president was very persuasive, but I'm looking for facts," said Rep. John Murtha, D-Pennsylvania, chairman of the House Defense Appropriations Subcommittee. Murtha questioned if the situation in Afghanistan is a threat to U.S. national security and said: "I'm looking for how we can live with this thing. We've got plenty of problems here in the United States."
U.S.-led troops invaded Afghanistan after al Qaeda's September 11, 2001, attacks. The invasion overthrew the ruling Taliban, which had allowed al Qaeda to operate from Afghanistan, but most of the top al Qaeda and Taliban leadership escaped.
Taliban fighters have regrouped in the mountainous region along the Afghan-Pakistan border. Al Qaeda's Osama bin Laden and Ayman al-Zawahiri are believed to be hiding in the same region.
The conflict has claimed the lives of more than 900 Americans and nearly 600 allied troops.
"A stable security situation in Afghanistan and Pakistan, one that is sustainable over the long term by their governments, is vital to our national security," Gates said.
"By the same token, the current status quo in Afghanistan -- the slow but steady deterioration of the security situation and growing influence of the Taliban -- is unacceptable."
The response from Kabul was positive.
"The U.S. president's speech was very important," said Afghan Foreign Minister Dadfar Rangin Spanta on Wednesday. "Mr. Obama said that the United States will take the necessary steps to help Afghanistan."
Insurgents, however, warned against the influx.
"The troop increase is a bad idea, and more U.S. soldiers will die because of it," said Taliban spokesman Zabiullah Mujahid, who accused Obama of political pandering.
Facing opposition from many in his liberal base, Obama cited the security threat to the U.S. and its allies to explain the need to increase troops. He also said he would ask NATO allies for additional troops.
At the same time, Obama included an early date to begin withdrawing forces to signal that the U.S. commitment would not be endless.
"Just as we have done in Iraq, we will execute this transition responsibly, taking into account conditions on the ground," Obama said Tuesday night. "We will continue to advise and assist Afghanistan's security forces to ensure that they can succeed over the long haul.
"But it will be clear to the Afghan government -- and, more importantly, to the Afghan people -- that they will ultimately be responsible for their own country."
The additional 30,000 troops would begin deploying early next year at "the fastest pace possible," Obama said.
Gen. Stanley McChrystal, who requested up to 40,000 more troops more than three months ago, praised the announcement, saying the president provided him with a clear mission and the necessary resources.
Obama said the additional U.S. forces bolstered by NATO troops "will allow us to accelerate handing over responsibility to Afghan forces and allow us to begin the transfer of our forces out of Afghanistan in July of 2011."
The strategy also focuses on helping Pakistan, with Obama saying, "There is no doubt that the United States and Pakistan share a common enemy."
"We will strengthen Pakistan's capacity to target those groups that threaten our countries, and have made it clear that we cannot tolerate a safe haven for terrorists whose location is known and whose intentions are clear," Obama said.
CNN's Deirdre Walsh, Alan Silverleib, Atia Abawi, Ted Barrett, Tom Cohen, Ed Henry, Adam Levine, Suzanne Malveaux, Matt Smith and Barbara Starr contributed to this report.