WASHINGTON—The Obama administration is struggling to confront a central reality of the Afghanistan war it inherited—that more troops, more aid and a retooled strategy alone are not enough.

It wants to energize the effort with new ideas, too—and do it before American public patience runs out.

It’s a grim given that U.S. casualties are likely to increase in the months ahead as additional soldiers and Marines arrive to take on the Taliban in their southern strongholds. Already some prominent members of Congress —including from Obama’s own party—are questioning whether Afghanistan is a lost cause.

That concern may explain, in part, the decision Monday to sack Gen. David McKiernan as the top U.S. commander in Afghanistan and replace him with an officer known for innovative action, Lt. Gen. Stanley McChrystal. Pentagon chief Robert Gates said it was time for “new thinking and new approaches.”

Yet it seems unlikely the switching of commanders portends a new U.S. war strategy. Obama announced a revised plan just two months ago. Instead the administration is hoping that a military command shake-up will lead to a more effective implementation of the existing strategy, which is aimed at defeating al-Qaida terrorists in Afghanistan and Pakistan and preventing their return to either country.

William Fallon, the retired Navy admiral who was responsible for U.S. military operations in Afghanistan and the broader Middle East in 2007-08, is optimistic that new leadership will make a difference.

“I have the highest confidence in his judgment,” Fallon said of McChrystal. “He gets it.”

The change at the top in Afghanistan won’t mean new marching orders for arriving Marines, said Lt. Gen. Dennis J. Hejlik, a U.S.-based Marine commander. However, Hejlik, too, suggested that McChrystal will do things differently.

“He really does understand that you’re not going to win the war by killing all the enemy. That’s just not going to work,” he said.

McKiernan recently described the war as “stalemated, at best” in the southern part of Afghanistan where the Taliban are strongest. For months he has called for an increase in U.S. forces, but during the Bush administration his requests went unmet as Iraq dominated the White House’s focus.

Obama entered the White House promising to make Afghanistan and Pakistan the higher priority, arguing that stopping al-Qaida from launching new attacks was of greater strategic importance than the task in Iraq. He also said he would “not blindly stay the course” in Afghanistan and would regularly review his approach. Since then the situation— militarily and politically—has arguably gotten worse.