U.S. Army troops load a truck with their luggage as they prepare for the end of their tour on Nov. 14 in Kandahar, Afghanistan. The top American commander in the nation must decide how much and how quickly U.S. troops will withdraw. (Matt Cardy/Getty Images)

The United States is planning to base about 1,000 security personnel at the U.S. Embassy in Kabul after the formal end of the military mission in Afghanistan and may retain the ability to use attack planes to support local forces until then, according to the top American commander in the country.

Gen. John F. Campbell is weighing several major decisions that may determine how quickly U.S. troops will withdraw next year, how far they will go in helping Afghan forces fight and how many Americans will remain on the ground when President Obama leaves office.

The final size of the stay-behind presence at the embassy, expected to be far larger than a similar civilian-led office established when U.S. forces withdrew from Iraq in 2011, provides possible hints about the scale of the military and financial support that U.S. officials believe Afghanistan’s forces will require well into the future.

“What I owe my senior leadership is to come out here and take my own look and then provide that perspective back,” Campbell said in a phone interview from Afghanistan. “I’m doing that now.”

The U.S. deliberations reflect the scale of the challenges that remain in Afghanistan, where Taliban militants have been able to mount large-scale attacks and, in some instances, reverse hard-fought military gains.

Campbell spoke about seven weeks after the inauguration of new Afghan President Ashraf Ghani, which ended months of political wrangling and accusations of fraud between the Western-trained Ghani and Abdullah Abdullah, the former foreign minister who agreed to join a national unity government in a U.S.-brokered political deal. That long period of uncertainty held up a troop agreement needed to finalize the U.S. force after this year.

But there are already signs that Afghanistan’s grand political compromise may not last as Ghani struggles to quickly form a cabinet.

Campbell suggested that the political disputes may force him to ask the Obama administration for permission to slow the timeline for pulling remaining U.S. troops from Afghanistan.

Under a plan that Obama announced in May, the American troop presence will fall to 9,800 by Jan. 1 and to about 5,000 by the end of next year. When Obama leaves office in January 2017, virtually all of the U.S. troops who remain will be part of the security assistance office attached to the U.S. Embassy.

“Today I would tell you that I’m comfortable with the plan we have,” Campbell said. “But I’m going to look hard as we move forward . . . can we get at some of the same objectives we want to get after, or do we need more time?”

While Campbell, beginning his third tour in Afghanistan, said the withdrawal timeline is fixed, he suggested that he might recommend changes to the pace of the troop departures within the milestones established by the president.

He is also evaluating plans for the long-term American presence in Afghanistan and said the size of the security assistance office — currently slated to include 1,000 people — could change. Personnel assigned to that office would help manage U.S. military support to Afghanistan, including arms, supplies, and any efforts to train or advise Afghan forces.

“We’re taking a lot of lessons learned in Iraq on how they did it . . . and we’ll incorporate that into our planning,” Campbell said. Critics of Obama’s withdrawal of U.S. troops from Iraq in 2011 have blamed that decision for the collapse of Iraq’s security this summer, when Islamist militants took over a third of the country.

Much of Campbell’s decision-making will be informed by the performance of Afghan forces, which have been built from scratch since 2001. While far more effective than they once were, they lack key capabilities in logistics, air support and intelligence. They are also grappling with a casualty rate that a senior U.S. military official described as “not sustainable.”

One way to reduce Afghanistan’s casualties would be to provide its military and police forces with more backing from the air in 2015, a move that has drawn resistance from the White House.

This summer, the Taliban mounted attacks with as many as 1,200 fighters, levels not seen since 2008. U.S. attack aircraft, in some instances, played a critical role in helping the Afghans hold their ground. “The Afghan army and police came close to defeats that would have been crippling to morale,” said a former senior U.S. official who served in Afghanistan this summer and who spoke on the condition of anonymity to discuss sensitive military operations.

Some top Obama administration officials have maintained that after the formal end of combat operations, scheduled for Jan. 1, U.S. attack planes shouldn’t be used to support Afghan forces. “Airstrikes sound a lot like combat operations to people in the White House, especially if you have U.S. guys controlling them on the ground,” said the former senior official.

Campbell said he was still “working through all [the] authorities” regarding U.S. airstrikes, but he said he believed that U.S. planes would be able to fly missions to help Afghan forces that were in danger of being overrun by larger Taliban formations. “I believe I will have flexibility on the ground to make those decisions based on several factors,” he said.

His larger focus, though, is on building up the Afghans’ ability to provide air support to their own troops. Campbell played down the importance of the strikes, noting that U.S. planes flying close air support for Afghan forces dropped bombs during only about 7 percent of their missions. “Is [close air support] the thing that makes or breaks the Afghans? I would say absolutely not,” he said.

Another major issue for U.S. commanders is how many bases will remain at their disposal through 2015. Commanders had planned on keeping Kandahar Airfield, the largest and last major American base in the south, open for much of next year. Some NATO allies, however, have been slow to commit troops for 2015, forcing Campbell and other top U.S. officials to reevaluate whether they will have enough troops to man the airfield and other critical facilities in the country. A decision on the base is expected later this month, U.S. military officials said.