Standing in a plywood-walled command post before Gen. John R. Allen, the supreme allied commander in Afghanistan, the nervous-but-earnest young lieutenant cast his platoon’s task for the day in the grand terms of counterinsurgency strategy — the American military’s wartime playbook for the past several years. The goal of the platoon’s walk through a bazaar and meetings with village leaders, the lieutenant said, was for the Afghan government to be “seen as an effective governing body that gains legitimacy with the local population.”

Such ambition used to elicit enthusiastic praise from visiting generals. Not anymore.

“How are you going to create that as an end state?” Allen asked, making no effort to mask his deep skepticism.

Faced with an order from President Obama to withdraw 23,000 troops by the end of the summer, and the prospect of further reductions next year, Allen is hastily transforming the U.S. military mission in Afghanistan. Instead of trying to continue large U.S. counterinsurgency operations for as long as he can, he is accelerating a handover of responsibility to Afghan security forces. He plans to order American and NATO troops to push Afghans into the lead across much of the country this summer, even in insurgent-ridden places that had not been candidates for an early transfer.

“My instruction to my commanders is to get the [Afghans] into the fight,” Allen said in an interview. “The sooner I can get them there, while I still have the time and the combat power, the more I can catch them if they fall.”

Here in Ghazni province, where American forces will mount the last major offensive of the decade-long war over the next few months, he is narrowing long-held U.S. goals. Instead of trying to reform the Afghan government, protect the civilian population and conduct security operations until Afghan forces are ready to take over — all of which Americans sought to do as recently as last year — a newly arrived brigade from the U.S. Army’s 82nd Airborne Division plans to spend the summer attacking Taliban redoubts before departing in mid-September, regardless of whether Afghan soldiers are capable of holding their own.

Six other American generals have taken turns commanding the war since 2002, and each sought to strike a decisive blow against the Taliban. Stanley McChrystal used a 30,000-troop surge to conduct intensive counterinsurgency operations across the south. David Petraeus, who succeeded him, increased the frequency of nighttime operations against Taliban commanders. But it is the silver-haired Allen, widely regarded in the military as one of the sharpest strategic thinkers in a four-star uniform, who may have the greatest impact on Afghanistan’s future — and America’s legacy in the strife-torn nation.

Unlike his predecessors, who had the luxury of troops and money, he has been forced to triage. He has narrowed targets for the development of local government, the pursuit of graft and the development of the country’s economy. His pragmatic focus is on the one prerequisite for America to head to the exits, as defined by the White House: Afghan security forces that are strong enough to keep the Taliban, which continues to enjoy sanctuary in neighboring Pakistan, from toppling the Kabul government. Although much of the Afghan army remains raggedy, with weak leadership and persistent supply shortages, he is betting that shifting responsibility sooner will increase the odds that Afghans will be able to stand their ground once the U.S. presence shrinks.

Allen’s approach has disquieted some on Capitol Hill and in the Pentagon, but the general’s plan has found favor among Obama and many of his top advisers, in part because the aggressive shift of responsibility to the Afghans could make it easier for the president to withdraw additional U.S. troops next year. For the first time since Obama became president, White House aides have ceased complaining about the military command in Kabul.

Obama has offered a degree of praise for Allen that never was accorded to his predecessors. When Obama and Allen walked out of a lunch in the White House earlier this year, the president put his arm around the general, according to administration and military officials. “John Allen is my man,” Obama said to staffers waiting in an anteroom.

But the improved relationship hasn’t made Allen’s job any easier. His to-do list over the next several months is more complex than any previous commander in Kabul: He has to remove 23,000 troops — shuttering bases and reallocating supplies — during the peak summertime fighting season, while also accelerating the training of Afghan forces, deploying new teams of U.S. advisers to assist Afghan troops, and negotiating the terms of an enduring U.S. military presence with President Hamid Karzai’s government.

“John Allen faces an unprecedented challenge,” said retired lieutenant general David Barno, the top U.S. commander in Afghanistan from 2003 to 2005. “He’s fighting a full-up insurgency at the same time he’s withdrawing forces and changing the mission. It’s an immense task.”

Allen’s predicament has no equivalent in modern American warfare.

In Iraq, U.S. troops departed in a far less violent environment. In Vietnam, Creighton Abrams, the general who presided over America’s withdrawal, had more troops at his disposal and more time to transfer responsibility to local forces.

By the early 1970s, according to historian Lewis Sorley, South Vietnamese President Nguyen Van Thieu’s government was more effective, and the country’s army was more competent, than Karzai’s administration and the Afghan security forces are today. Allen “has a much more difficult job,” said Sorley, the author of “A Better War: The Unexamined Victories and Final Tragedy of America’s Last Years in Vietnam.”

Allen, 58, is an avid reader of military histories and sees the Vietnam analogies — the insurgent safe havens across a national border, the plummeting public support back home — but he is studying a different withdrawal: that of the Soviets from Afghanistan in 1989.

“We’re fighting on the same ground,” he noted.

Afghanistan’s Communist government remained in power through the pullout, falling only three years later, after the Soviet Union collapsed and its economic aid to Kabul ended. To Allen, that fact argues for sustained American assistance to Afghanistan, particularly to pay for its army and police, which will grow to a combined strength of 352,000 this year.

The annual price tag will be about $4 billion, a staggering cost, but far cheaper than the $100 billion annual tab to keep 100,000 American troops on Afghan soil. He and Obama plan to make the case for NATO to help foot the bill, and provide other long-term support to Afghanistan, during the alliance’s annual summit in Chicago next weekend.

Allen blazed an unconventional path to the wood-paneled commander’s office in Kabul. A native of Warrenton, Va., he attended the Flint Hill School in Oakton. He decided to apply to the U.S. Naval Academy after hearing his father, a Navy radio man who served aboard a destroyer that was torpedoed by a German U-boat in 1941, share tales of naval heroism.

Although Allen would go on to lead a Marine infantry company and a battalion, he never had sole command of a division-sized unit — a standard prerequisite to become a four-star wartime commander. Instead, his career has been filled with unusual accomplishments: He won a coveted leadership award given to only one Marine captain each year, and he became the first Marine to serve as the commandant of midshipmen at the Naval Academy.

He spent two years in Iraq’s Anbar province, but his focus was not on day-to-day operations; he spearheaded an effort to reach out to Sunni tribal sheiks and persuade them to stand against al-Qaeda militants — a shift that helped turn the course of the war in western Iraq.

He eventually became the deputy commander of the U.S. Central Command, where his portfolio focused largely on Iran. The job afforded him the opportunity to brief Obama, who grew impressed by the general’s analyses. When Obama appointed the previous commander in Kabul, Petraeus, to head the CIA, Allen was said to be a shoo-in for the post. To end America’s longest war, administration officials said, the president wanted someone with fresh ideas in Kabul.

Put aside the uniform and the 6-foot-tall Allen is more professor and Southern gentleman than hard-bitten Marine general. He is unfailingly polite and prone to measured locution. He devours tomes of military history while others are in bed — he sleeps only about four hours a night — and he sets aside several hours each week “to think about big ideas.”

When he was a brigadier general, he told Naval Academy students in a letter that he had been profoundly affected by reading classic military historians, among them Stephen Ambrose, John Keegan and Barbara Tuchman. “If my house were on fire and we were all running for our lives,” he wrote, “I would first save my family, and then all my volumes by these writers.”

He has not yet informed Obama, who has indicated that he wants to keep withdrawing forces next year, how many troops he believes should stay in Afghanistan through 2013, but he is not digging in his boots to maintain all of the 68,000 troops that will remain after the current drawdown phase is completed at the end of September.

By the end of the year, he predicted, “we could find that the operational environment for ’13 could be pretty significantly different,” although he said he will still need Special Operations forces, trainers for the Afghan troops and some conventional units to operate in areas not yet ready for transfer to Afghan control.

It is a very different method from that taken by Petraeus, who sought to push Obama, during war cabinet discussions in 2011, to delay the drawdown until the end of this year so that U.S. forces could continue large-scale counterinsurgency missions. Petraeus failed. But Allen did manage to persuade Obama, in private discussions, not to announce any additional troop cuts until he provides a range of options to the White House in late fall.

To those in the two-story yellow building that houses the NATO headquarters in Kabul, Allen’s approach to the troop reductions reflects his leadership style.

Under Petraeus, “it was much more of a one-man show. There was much less oxygen for debate,” said a senior NATO official who spoke on the condition of anonymity to describe the two generals. “John Allen listens a lot more carefully to what people are saying to him.”

When Allen arrived in Kabul last July, the U.S. and NATO war plan called for a gradual transition of territory to Afghan control by the end of 2014, the point at which NATO’s combat mission will end. Based on the assumption that the United States would maintain substantial combat power in the country until then, the strategy envisaged the most violent, Taliban-saturated places to be handed over last, allowing U.S. troops maximum time to conduct counterinsurgency operations.

To Allen, that plan didn’t reflect the new reality in Afghanistan — or Washington. Afghan military leaders wanted to assume more responsibility, and it seemed unlikely Obama would be willing to forestall additional drawdowns until 2014. As Allen chewed through his options, he concluded that he needed to upend the strategy: Instead of waiting until the very end to transition the toughest places, he would “front-load risk” and allow Afghans to take charge of those areas sooner.

The next set of districts and provinces to be transitioned to Afghan control will be announced in the coming weeks and it will contain several areas — including districts around the city of Kandahar—that remain insurgent battlegrounds. By handing off violent areas sooner, Allen said, it will thrust Afghans into a lead role while the U.S. military still has enough forces to come to their rescue, if needed. And it means that the final two rounds of transition will be far less challenging.

“I seek as much as I can to mitigate risk,” he said.

The accelerated transition comes with a cost. The original plan involved waiting until not just security had improved but local governments had been established and economic development had commenced. The new approach essentially jettisons governance and development goals. “The time scale for their delivery is not the same scale we’re working on for the security transition,” the senior NATO official said.

The 82nd Airborne’s upcoming Ghazni operation also reflects the new American way of war in Afghanistan. Soon after Obama took office in 2009, U.S. commanders vowed they wouldn’t transition areas to Afghan control until coalition forces had cleared those places of insurgents, held that ground and then built a functioning government and economy. But the newly arrived brigade will spend only five months on the ground; its soldiers must leave Afghanistan before the Sept. 30 drawdown deadline.

“We’re going straight from clear to transition,” one of Allen’s subordinate generals said, speaking on the condition of anonymity. “This is the last real glass-breaker where we exert our will. But then it’ll be up to the Afghans.”

Allen doesn’t intend to let the Afghan army fend for itself. Each battalion will have a small team of U.S. or NATO advisers who can summon air and artillery strikes, provide intelligence from drones, defuse roadside bombs and request medical evacuations. But U.S. military officials believe the Afghan army still has a long way to go before it can operate at top form, even with mentors. Only 18 of the country’s 293 battalions have been deemed by the Americans to be capable of independent operations with coalition advisers.

Some battalions have been plagued by poor leadership and weak morale. Others have been hindered by basic logistical challenges. When Allen visited the forward operating base in Qara Bagh, he asked about the status of the Afghan army battalion in the area. He was told that it had 100 percent of its assigned personnel, but the unit had only six working Humvees of the 28 it had been assigned. The problem was maddeningly simple: Nobody in the battalion had requisitioned the necessary spare parts from the supply depot.

The fast handover to Afghan forces is but one reminder of America’s diminished ambition. His other principal challenge is figuring out how to remove 23,000 troops by September. About 10,000 of them will be Marines from Helmand province, where violence has dropped significantly since the United States commenced large counterinsurgency operations in mid-2009; the rest will have to come from other parts of the country that are far less secure. For Allen and his top deputies, it is a process of trade-offs, of least-worst options. There are no good answers, even with their plan to hand off more responsibility to the Afghans.

“Petraeus had all the fun of building it up,” said Simon Gass, a British diplomat who serves as NATO’s senior civilian representative in Afghanistan. “John Allen has all the challenges of tearing it down.”

Late in the evening of April 25, Allen received a nightly summary of casualties across the country. The tally from southern Afghanistan was unusually high: two killed in action and 16 more wounded, several of them seriously, over the previous 24 hours. Allen decided to cancel his meetings the next morning and head to Kandahar.

He would spend just 30 minutes there, all of it at the base hospital, walking from bed to bed in the intensive care unit, bending over the wounded and putting his hand on their head or shoulder, and whispering words of encouragement.

Thank you for all you have done.

Take care of yourself.

You’re one tough guy.

Then he pressed a gold-rimmed commemorative coin in their palms.

“Every one of these counts in a big way to me,” Allen said a few days later. “On that morning, that was where I needed to be.”

Allen is painfully aware that two-thirds of Americans no longer believe the Afghan war is worth fighting. He had hoped that his testimony before the House and Senate armed services committees in early April would help change minds, but “it didn’t penetrate.”

He recognizes that his war has far more modest goals than some of his predecessors envisioned. But it is not a hasty run to the exits. It is, he hopes, withdrawal and transition with honor — a decent ending to a long, grueling conflict that has claimed almost 2,000 American lives and left thousands more with severe, permanent injuries.

“I can’t spend a lot of time worrying about the numbers at home,” he said. “I’ve got to focus on the mission.”

Allen is convinced that his campaign ultimately will be successful, even if it may not appear to be a clear-cut victory. But, he cautioned, “it’s going to be hard as hell.”

Allen assumed his days would be consumed with the Afghan handover and the drawdown, not to mention all of the other chores has predecessors faced — the meetings with congressional delegations and defense ministers from 50 coalition nations, the regular sessions with Karzai and his security ministers, and the vexing problem of insurgent sanctuaries in Pakistan.

What he didn’t count on were what his staff calls “meteor strikes”: the release of a video showing Marines urinating on Taliban corpses; the burning of Korans at a giant U.S. base outside Kabul; and an Army sergeant’s allegedly murderous rampage near Kandahar. Each has thrown Allen and his staff for a loop, consuming hundreds of hours of time that could have been devoted to other tasks. And they have complicated his relationship with Karzai, increasing Afghan leverage in negotiations over restrictions on nighttime raids and a transfer of prisoners to Afghan control.

Those who have attended meetings between Allen and Karzai said the general has sought to strike a polite but firm tone in the face of the president’s anger, navigating a middle ground between McChrystal’s deference to the Afghan leader and Petraeus’s forcefulness. “Allen has exercised an approach of astonishing patience under provocation,” a senior Western diplomat in Kabul said.

After Karzai complained about “twin demons” in his country, referring to the Taliban and international forces, Allen wanted to fire back. But he forced himself to seethe quietly in the presidential palace. Then, when he returned to Washington, he made clear how he felt: “I reject the equivalence of our forces with the Taliban,” he told the Senate Armed Services Committee.

“I’ll take it to a point,” he said over dinner in Kabul, “but I won’t take it to a fault.”

When Allen traveled to Ghazni, he had lunch with a dozen junior officers from the 82nd Airborne’s 1st Brigade. Instead of exhorting them to make the most of the last major U.S. operation of the war — telling them that the next several months would be America’s final chance to flush the Taliban from the province’s 7,000-foot plains — the general launched into a lecture about small-unit leadership.

“I need for our standards to be inviolate. We all know what’s right,” he said as the lieutenants and captains ate roast beef and noodles from Styrofoam containers. “This war can be lost without the Taliban winning. We have to win this morally as well as tactically and operationally.

“We want them to miss us because we were special to them. We don’t want them wiping their brows and saying, ‘Thank God they’re gone.’”