U.S. President Barack Obama's plan to beef up troop levels in Afghanistan has won the approval of his top military commander in that country, though critics at home and abroad say it is unclear whether he has unveiled a roadmap to ultimate success.

Obama announced Tuesday evening that he will send 30,000 more U.S. troops into Afghanistan next year, to resuscitate a deteriorating state of affairs and to speed up the process of handling over responsibility to Afghan security forces.

The president said the U.S. could start pulling its troops out of the war-torn country as soon as July 2011, but only if the conditions are right. And he reiterated that the United States' core goal is to disable the al Qaeda terror network.

Shortly after the announcement, U.S. Gen. Stanley McChrystal said he was "absolutely supportive of the timeline" outlined by the president. He said the remaining time would be used to shore up the capabilities and build the confidence of the Afghan troops who will be in charge of security when NATO and U.S. troops leave.

McChrystal said the U.S. and its partners need to break the will of the Taliban to convince them that they cannot win. And they must "convince them that the reasons that they are participating are not valid," by tackling corruption and improving governance.

Scott Taylor, the editor of Esprit de Corps magazine, said Obama's decision to increase troop levels was undoubtedly influenced by an August report from McChrystal that suggested the war was "deteriorating" and could be lost without additional backup.

That report, which was leaked to the Washington Post in late September, put pressure on the president to listen to the general's concerns, Taylor said.

"Ultimately, Barack Obama didn't have much of a choice if he doesn't want to be the president who lost the war," he told CTV's Canada during an interview from Ottawa on Tuesday morning.

The shift in U.S. troop levels comes immediately after NATO announced new plans to redistribute the existing soldiers working in Afghanistan. Americans will be assuming responsibility for the security of the area surrounding Kandahar city, while Canadians will take over the security just north of that city in the Arghandab district.

Critics question troop withdrawal timeline

Alex Their, of the United States Institute for Peace, said the president made a compelling case to the American people for the continued and increased use of the U.S. military in Afghanistan. But it is unclear if they are convinced that the U.S. can be successful.

"I think that the critical piece that probably needs more emphasis is the civilian side -- not only how do we deal with the security challenge of the Taliban, but how do we ultimately build an Afghan government that is strong enough to stand on its own," he told Canada AM during an interview from Washington.

Retired general Tom Wilkinson, now with the U.S. Naval Institute, told CTV News Channel's Power Play that Obama's speech was the most difficult of his career but riddled with "contradictions"

"What happens when we begin the withdrawal?" he asked. "If you are wearing the enemy's clothes, and you heard the president's address, chances are you would say, 'That's terrific, all I have to do is hide until 2011and let things follow their course.'"

However, as Obama never detailed the nature of the pullout, some observers say that suggests a very gradual withdrawal that could extend far beyond 2011 and one that could affect the Canadian withdrawal.

"The United States has given itself a degree of flexibility . . . Canadians are locked in to the end of the combat mission by 2011, and frankly, they are going to have to start thinking about that now, as they can't be the first to the exits," Wesley Wark of the Munk Centre for International Studies at the University of Toronto, told Power Play.

"They are going to have to align themselves to what might be a much more gradual American draw-down of troops from 2011 on."

In the Afghan government, Interior Minister Hanif Atmar lauded Obama's speech but said the 18-month timeframe was too short.

"That kind of time frame will give us momentum," Atmar said. "We are hoping that there will be clarity in terms of long-term growth needs of the Afghan national security forces and what can be achieved in 18 months."

With files from The Associated Press