After the Sept. 11 attacks, the United States shifted resources to fighting terrorism. While most of those were focused on groups like Al Qaeda and then the Islamic State, both with the reach to orchestrate or inspire attacks on the United States homeland, American military and intelligence agencies also built up resources against regional terrorism threats.

The Trump administration, hoping to prevent the United States from becoming entangled in more long wars, wants the military and intelligence forces to scale down their ambitions. Under the plans now being discussed, fewer resources would be allocated to monitoring regional threats — terrorist groups that might spout anti-American speech but do not have the wherewithal to mount a significant attack on United States territory.

Mr. Rasmussen said no terrorist organization in Africa so far had successfully been able to attack the American homeland, giving credence to the idea that too much emphasis had been put on such groups. But without military and intelligence personnel on the ground, working with partner nations to help combat regional terrorist organizations, it becomes difficult to assess which groups have or could have the capabilities to mount an attack on the United States, Mr. Rasmussen said.

“If our intelligence picture is degraded significantly by a drawdown in presence, we run the risk of failing to collect that critical bit of intelligence that might give us insight on the capability part of the equation,” Mr. Rasmussen said.

The shift, military and intelligence officials said, is also part of an effort to move resources toward countering the rise of China and to more adroitly compete with Beijing.

But some American officials believe that cutting back the intelligence and military presence will reduce the United States’ clout in Africa at the very time it is becoming a front line in the influence battle with Russia and China.