Officials said that the Pentagon’s proposed new architecture of bases would include four “hubs” — including expanding existing bases in Djibouti and Afghanistan — and smaller “spokes,” or more basic installations, in countries that could include Niger and Cameroon, where the United States now carries out unarmed surveillance drone missions, or will soon.

The hubs would range in size from about 500 American troops to 5,000 personnel, and the likely cost would be “several million dollars” a year, mostly in personnel expenses, Pentagon officials said. They would also require the approval of the host nation.

The military already has much of the basing in place to carry out an expansion. Over the past dozen years, the Pentagon has turned what was once a decrepit French Foreign Legion base in Djibouti, in the Horn of Africa, into a sprawling headquarters housing 2,000 American troops for military operations in East Africa and Yemen.

Similarly, the American military has been using a constellation of airstrips in Africa, including Ethiopia and Burkina Faso, for surveillance missions flown by drones or turboprop planes designed to look like civilian aircraft, to collect intelligence about militant groups across the northern part of the continent.

The Pentagon plan also calls for a hub in the Middle East, possibly Erbil, in northern Iraq, where many of the 3,500 American troops in Iraq are based.

The new approach would try to bring an ad hoc series of existing bases into one coherent system that would be able to confront regional threats from the Islamic State, Al Qaeda or other terrorist groups — including possible attacks against American embassies, like the assault on the diplomatic compound in Benghazi, Libya, in 2012. It would also ensure that the bases would receive regular financing in the annual Pentagon budget and it could lengthen — and make more predictable — troop deployments, especially among Special Operations forces who often rotate assignments every several months.