CHARBARAN, Afghanistan » The first helicopter landed in the bluish gray gloom before dawn. More than 20 members of a U.S. reconnaissance platoon and Afghan troops accompanying them jogged out through the swirling dust, moving into a forest smelling of sage and pine.

Three more helicopters followed, and soon roughly 100 troops were on the floor of this high-elevation valley in Paktika province, near the border with Pakistan. They were beginning their portion of a brigade-size operation to disrupt the Haqqani network, the insurgent group that collaborates with the Taliban and al-Qaida and has become a primary focus of U.S. counterterrorism efforts since Osama bin Laden was killed.

The group, based in Pakistan’s northwestern frontier, flows fighters into Afghanistan and has orchestrated a long campaign of guerrilla and terrorist attacks against the Afghan government and its U.S. sponsors.

Its close ties to Pakistan’s intelligence service, and Pakistan’s unwillingness to act against the Haqqani headquarters in Miram Shah, a city not far from the Afghan border, have drawn condemnation from Washington and escalated tensions between two nations that officially have been counterterrorism partners.

Against this backdrop, the helicopter assault into Charbaran this past week highlighted both the false starts and the latest set of urgent goals guiding the U.S. military involvement in Afghanistan.

The Pentagon plans to have withdrawn most of its forces from the country by 2014. Talk among many officers has shifted sharply from discussions of establishing Afghan democracy or a robust government to a more pragmatic and realistic military ambition: doing what can be done in the little time left.

In the tactical sense, this translates to straightforward tasks for units in the security buffer along the border. While they still have their peak troop presence, U.S. commanders are trying to bloody the strongest of the armed anti-government groups and to put thousands more Afghan police officers and soldiers into contested areas.

The long-term ambition is that Afghan forces will have the skills and resolve to stand up to the insurgency as the Americans pull back.

And yet, even while looking beyond 2014, U.S. units must fight a day-to-day war.

One element lies in trying to prevent more of the carefully planned attacks that have shaken Kabul, the Afghan capital, several times this year. The attacks — striking prominent targets, from the capital’s premier hotel to the U.S. Embassy — have often been organized by the Haqqanis, and have highlighted the Afghan government’s vulnerability and the insurgents’ resiliency.

Lt. Col. John V. Meyer, who commands the Second Battalion of the 28th Infantry Regiment, which used two companies to cordon off the Charbaran Valley and another to sweep the villages, called the operation "a spoiling attack to prevent a spectacular attack in the Kabul area." It was also intended, he said, to gather intelligence.

The Charbaran Valley has become one of the main routes for Haqqani fighters to enter Afghanistan. They generally come in on foot, U.S. officers say, and then, after staying overnight in safe houses and tent camps, they work their way toward Kabul or other areas where they have been sent to fight.

Mid-level Haqqani leaders also meet in the valley’s villages, U.S. officers said, including near an abandoned school and the ruins of a government center that the United States built earlier in the war but that local fighters had destroyed by 2008.

It was 2010 when the last conventional unit entered the valley. An infantry company, it landed by helicopter and was caught in a two-hour gunfight as it left.

When the U.S. and Afghan troops fanned out this time, their mission faced a familiar law of guerrilla war: When conventional forces arrive in force, guerrillas often disperse, setting aside weapons to watch the soldiers pass by.

The operation was also probably no surprise to the Haqqani fighters in the valley, U.S. officers said, because during the days of preparation some of the Afghan troops probably leaked that the assault was coming.

As the soldiers climbed the hills — laden with body armor and backpacks heavy with water and ammunition — they almost immediately found signs of the fighters’ presence.

Throughout the operation, hidden fighters were occasionally heard over the two-way radios that Afghan interpreters were monitoring for intelligence. The guerrillas had threatened to ambush the reconnaissance company.

After the U.S. and Afghan soldiers reached the opposite slope, the guerrillas managed their only attack: They fired four mortar rounds from outside the cordon.

The rounds exploded well behind the soldiers, near the abandoned school, causing no harm but making clear that Charbaran, which had fallen almost silent as the company moved through, remained out of government hands.