In an interview with The New York Times in July, Gen. Thomas D. Waldhauser, head of the Africa Command, said other training teams could still rotate in periodically for days or weeks of instruction if the Pentagon reduced its permanent troop presence in Africa.

He said those teams could be brought in from National Guard units from California, Indiana, Michigan and other states.

“We won’t walk away and abandon this,” General Waldhauser said.

The defense strategy that was unveiled in January, coupled with the deadly attack in Niger, has fast-tracked decisions by Mr. Mattis and Gen. Joseph F. Dunford Jr., the chairman of the Joint Chiefs of Staff, to end some of the missions in Africa, military officials have said.

General Dunford and Mr. Mattis, a former four-star Marine general, had little experience working directly with commando units when they were younger officers progressing up the chain of command. That has fostered an institutional skepticism about the American military’s increasing reliance on Special Operations Forces in recent years, like those spread across Africa.

In the interview, General Waldhauser said that other combatant commands, such as those that cover the Middle East and the Pacific, will face similar changes. But one Defense Department official familiar with the deliberations said the Pentagon’s changes would largely affect the Africa Command, which was created only in 2007, years after the wars in Iraq and Afghanistan got underway.

Another Defense Department official said the move to close the commando outposts would greatly diminish American influence in Africa and could prove to be shortsighted.

The first official, however, said local African forces had become increasingly capable in fighting extremists on their own, and do not need permanent assistance from American troops, at least in some areas. Additionally, that official said, the American commandos could return if necessary.