KABUL, Afghanistan - "We are in this to win," Gen. David Petraeus said as he took the reins of an Afghan war effort troubled by waning support, an emboldened enemy, government corruption and a looming commitment to withdraw troops - even with no sign of violence easing.

Petraeus, who pioneered the counterinsurgency strategy he now oversees in Afghanistan, has just months to show progress in turning back insurgents and convince both the Afghan people and neighboring countries that the U.S. is committed to preventing the country from again becoming a haven for al-Qaida and its terrorist allies.

"We are engaged in a contest of wills," Petraeus said Sunday as he accepted the command of U.S. and NATO forces before several hundred U.S., coalition and Afghan officials who gathered on a grassy area outside NATO headquarters in Kabul.

Petraeus, widely credited with turning around the U.S. war effort in Iraq, said the Taliban and their allies are killing and maiming civilians - even using "unwitting children to carry out attacks" - in an attempt to undermine public confidence in the Afghan government and the international community's ability to prevail.

"In answer, we must demonstrate to the people and to the Taliban that Afghan and international forces are here to safeguard the Afghan people, and that we are in this to win," Petraeus said on the Fourth of July, U.S. Independence Day.

Continual discussion about President Barack Obama's desire to start withdrawing U.S. forces in July 2011 has blurred the definition of what would constitute victory. That coupled with the abrupt firing of Petraeus' predecessor, a move that laid bare a rift between civilian and military efforts in the country, has created at least the perception that the NATO mission needs to be righted.

June was the deadliest month for the allied force since the war began, with 102 U.S. and international troops killed. Progress in stabilizing Taliban strongholds in the south has been slow, support for the war is waning in the United States and allied nations, and doubts persist about the Afghan government's willingness and ability to fight corruption.

"After years of war, we have arrived at a critical moment," Petraeus said. "We must demonstrate to the Afghan people - and to the world - that al-Qaida and its network of extremist allies will not be allowed to once again establish sanctuaries in Afghanistan from which they can launch attacks on the Afghan people and on freedom-loving nations around the world."

Petraeus suggested he would refine, or at least review, the implementation of rules under which NATO soldiers fight, including curbs on the use of airpower and heavy weapons if civilians are at risk, "to determine where refinements might be needed."

Some troops have complained that such restraint puts their own lives in danger and hands the battlefield advantage to the Taliban and their allies.

"Protecting those we are here to help nonetheless does require killing, capturing or turning the insurgents. We will not shrink from that," Petraeus wrote Sunday in a memo to his troops. But he added when they got into tough situations, NATO must "employ all assets to ensure your safety, keeping in mind, again, the importance of avoiding civilian casualties."

The rules aimed at protecting civilians were put in place under Petraeus' predecessor, Gen. Stanley McChrystal, who was dismissed last month for intemperate remarks he and his aides made to Rolling Stone magazine about Obama administration officials - mostly on the civilian side.

Petraeus praised McChrystal early in his 10-minute speech. "The progress made in recent months - in the face of a determined enemy - is in many respects the result of the vision, energy and leadership he provided," he said.

In an effort to move past the rifts between the civilian and military camps, Petraeus reiterated the message he delivered Saturday at the U.S. Embassy: "Cooperation is not optional."

The new commander said everyone had worked hard during McChrystal's tenure in Afghanistan to carry out an effective civilian-military counterinsurgency, one that Petraeus pioneered in Iraq.

Petraeus also sought to counter skepticism, even defeatism, that was on display last month during hearings in Washington when lawmakers challenged Pentagon assertions that progress was being made in the war.

He acknowledged the fight in Afghanistan has been grueling, but insisted progress had been made: 7 million Afghan children in school compared with fewer than 1 million a decade ago; child immunization rates at 70 percent or higher; new roads; and bustling economies in several cities.

When announcing the 2011 target, Obama was careful to say any pullout decisions would be based on improved security. Yet that caveat has often been forgotten.

Obama's timetable has provided the Afghan government the impetus to implement reforms and bolster governance deeper into the provinces. But it also fueled fears in Afghanistan that the U.S. commitment was fading in the almost nine-year-old war.