Smoke billows from the scene of a suicide bomb blast that targeted a police headquarters in Kunduz, Afghanistan, on Feb. 10, 2015. Five Taliban fighters were killed in the attack. (Jawed Karger/European Pressphoto Agency)

The Obama administration is considering slowing its planned withdrawal from Afghanistan for the second time, according to U.S. officials, a sign of the significant security challenges that remain despite an end to the U.S. and NATO combat mission there.

Under the still-evolving plans, Army Gen. John F. Campbell, the commander of U.S. and NATO forces in Afghanistan, could be given greater latitude to determine the pace of the drawdown in 2015 as foreign forces scramble to ensure Afghan troops are capable of battling Taliban insurgents on their own, the officials said.

The options under discussion would not alter what is perhaps the most important date in President Obama’s plan: ending the U.S. military mission entirely by the time he steps down in early 2017.

But officials said Campbell might temporarily retain more than the 5,500 troops slated to remain in Afghanistan at the end of 2015, keep regional training hubs open longer than planned or reorganize plans to close bases including Kandahar Airfield, a major endeavor that would draw troops away from efforts to advise Afghan security forces.

Campbell and top Obama aides are expected to discuss the options at a White House meeting Wednesday.

“The defining elements of the plan are more or less intact,” a senior administration official said, speaking on the condition of anonymity to discuss planning. “All we’re looking at at this point is either variations within those or subtle variations of” the current framework.

Officials hope to finalize a decision before Afghan President Ashraf Ghani visits Washington in March. Ghani has appealed to Obama to “reexamine” his drawdown schedule.

“We are cognizant of the fact that we’ve got to get in front of the so-called spring fighting season in Afghanistan” and provide allies time to make their own troop plans, the official said.

Campbell already faces a tight timeline for the twin mission he commands in Afghanistan, a NATO effort to advise Afghan security forces and a separate U.S. program that conducts limited operations against al-Qaeda and other militants.

Obama announced the White House’s drawdown plan in May 2014, before the onset of a lengthy electoral dispute in Kabul that deepened questions about the country’s stability after foreign forces go home.

The dispute also held up troop deals needed to launch the current training mission and made it harder for NATO nations to commit their own troops on time.

The drawdown schedule has been adjusted previously. In December, Defense Secretary Chuck Hagel announced during a visit to Kabul that the United States would keep as many as 10,800 troops in Afghanistan into early 2015, 1,000 more than had been expected to remain at the time the NATO combat mission concluded on Dec. 31, 2014.

The U.S. force in Afghanistan, which peaked at about 100,000 troops during Obama’s surge in 2011, stands at about 10,600 U.S. service members.

Last fall, the White House also decided to expand some authorities for remaining U.S. troops to fight militants after the NATO combat mission ended.

It remains unclear whether Obama will ultimately approve another deviation from the plan he announced with great fanfare in the White House Rose Garden.

While the Democratic president has sought to end U.S. involvement in messy conflicts overseas, he has also associated himself with the Afghan war, launched in the aftermath of the Sept. 11, 2001, attacks. The adjustment announced in December, moreover, triggered little criticism at a time when foreign-policy leaders also were grappling with crises in Ukraine, Iraq, Syria and elsewhere.

Officials said the current discussions were rooted in an appeal from Ghani, whose security forces lack air power and key military skills as they face insurgents whose zeal and ability to launch attacks from neighboring Pakistan remain undiminished.

U.S. officials also believe a larger force could help protect troops from excessive risk. Late last month, three American contractors were killed at the Kabul airport by a man in Afghan security forces uniform, a reminder of the “insider threat” that U.S. troops have faced in Afghanistan.

David S. Sedney, a former senior Pentagon official specializing in Afghanistan policy, said that a rapid reduction in U.S. forces in 2015 also could fuel greater casualties among Afghan forces, which have taken heavy losses in clashes with the Taliban, by depriving them of U.S. air support, intelligence and logistics when they continue to confront a powerful adversary.

“It’s hugely counterproductive to have this timeline for 2015 laid out the way it is,” Sedney said. Campbell’s troops “are going to be of very little use if they’re straitjacketed by a 50-percent cut halfway through the year.”

Rear Adm. John Kirby, a Pentagon spokesman, said there had been no change to plans for withdrawing troops over the next two years. “As always, the operational commander has the right and responsibility to manage the pace of that withdrawal as he deems fit,” he said.

In recent months, there has been growing support within the Pentagon to empower Campbell to respond to conditions on the ground in Afghanistan.

Army Gen. Martin E. Dempsey, chairman of the Joint Chiefs of Staff, has voiced support for reviewing the drawdown schedule according to the situation in Afghanistan. Last week, Ashton B. Carter, who has been nominated to replace Hagel as defense secretary,expressed openness to revising the current plan.

“Flexibility remains important as we continually assess both the progress and the threats in Afghanistan,” a senior military official said, also speaking on the condition of anonymity. “But that does not imply an open-ended commitment of troops is in either their interest or ours. We’re on the right path, and we’ll make recommendations in the margin as needed.”

The deliberations take place as Campbell visits Washington to answer senators’ questions about the U.S. campaign in Afghanistan.

The discussions also coincide with growing concerns that security could deteriorate in Afghanistan after the U.S. exit, as it did in Iraq, where Islamic State militants seized a third of the country last year and forced Obama to renew military operations there.

Karen DeYoung contributed to this report.