Spc. Gavin Fruge, 22, of Crowley, La., left, and fellow soldiers watch President Obama's speech from at Kandahar Airfield in Afghanistan. (AP)

The withdrawal of 33,000 U.S. troops from Afghanistan by next summer signals a coming shift in both where and how the war has been fought over the past two years.

The “surge” troops President Obama deployed last year have been concentrating on battling the Taliban in the flat, desert south through a counterinsurgency strategy that requires intensive investments of money and personnel.

But Obama, making a virtue of necessity fueled by budget constraints, a restive Congress and faltering public support, has now declared those areas sufficiently stabilized to begin lowering the U.S. profile there.

“We are starting this drawdown from a position of strength,” he said Wednesday night.

The same cannot be said of the Afghan east, where the fight is more about killing declared enemies than pacifying broad swaths of the population in a nation long defined by instability.

Although the east has been a secondary focus of U.S. attention compared with the Taliban heartland in southern Afghanistan, some of the insurgency’s most vicious fighters, along with the forces most directly tied to al-Qaeda, hold sway in the rugged eastern mountain valleys and have made increasing inroads from their havens in Pakistan, which borders these provinces.

The east, one military official said, has always presented a “tougher kinetic fight” than the south.

Meanwhile, in Pakistan, CIA operations against al-Qaeda senior figures and hideouts have become more difficult as U.S.-Pakistani relations have worsened following the U.S. commando raid last month that killed Osama bin Laden in his Abbottabad compound.

“It is a different fight, and it has been for some period of time,” said Senate Foreign Relations Committee Chairman John F. Kerry (D-Mass.), who has urged a greater focus on eastern Afghanistan and on Pakistan.

“The president talks about [insurgent] sanctuaries,” Kerry said in an interview after Obama’s address. “That is where almost all the mischief comes from. If we can change that equation . . . that is the best opportunity to protect what we have gained in Afghanistan.”

Although the administration has denied any shift in the strategy that Obama announced in December 2009, a renewed focus on the east will amount to a de facto change in the balance between the counterinsurgency tactics that have been central to the southern mission and the targeted counterterrorism that has marked U.S. operations in eastern Afghanistan and Pakistan. The switch has long been advocated by many within the White House, including Vice President Biden.

Gen. David H. Petraeus, the outgoing coalition commander in Afghanistan, was already planning an increase in forces in the eastern provinces, although he had hoped to be able to shift them from the south without an early decrease in the overall number of U.S. troops.

One of the reasons Obama has had difficulty in sustaining support for his Afghan strategy has been the absence of al-Qaeda from the southern battlefields, which has raised questions about why the United States is fighting in Afghanistan. But if the administration identifies the fight more directly with the battles in the east and in Pakistan, the case for the war is likely to be easier to make.

In his speech, Obama began to do so, saying that “the goal that we seek is achievable and can be expressed simply: no safe haven from which al-Qaeda or its affiliates can launch attacks against our homeland or our allies. We will not try to make Afghanistan a perfect place. . . . Of course, our efforts must also address terrorist safe havens in Pakistan.”

While numerous international terrorist plots have emerged from Pakistan in recent years, “we haven’t seen a terrorist threat emanating from Afghanistan for the past seven or eight years,” a senior administration official said.

“There has been clearly fighting and threats inside of Afghanistan, but the assessment of anywhere between 50, 75 or so al-Qaeda types that are embedded in Haqqani [insurgent] units . . . are focused inside Afghanistan, with no indication at all that there is any effort . . . to use Afghanistan as a launching pad to carry out attacks outside of Afghan borders,” the official said.

U.S. forces in the southern Afghan provinces of Kandahar and Helmand have been fighting Taliban members loyal to Mohammad Omar, the leader of the former Taliban government that fled into Pakistan’s Baluchistan province. The separate Haqqani network of Afghan militants is based in Pakistan’s federally administered tribal regions, along Afghanistan’s eastern border.

Haqqani sanctuaries — from which attacks are launched throughout eastern Afghanistan — are most closely intertwined with those belonging to al-Qaeda; together, they have been the primary targets of drone-launched CIA missiles in Pakistan.

The current estrangement between the United States and Pakistan — including Pakistani demands that the CIA withdraw from the base where many of the drones are based — has also helped convince administration officials of the importance of expanding the U.S. military presence in eastern Afghanistan.

“We will work with the Pakistani government to root out the cancer of violent extremism,” Obama said, “and we will insist that it keep its commitments.”