MANTA, Ecuador — When U.S. officers stationed in this humid coastal city give reasons they should continue their decade-old airborne surveillance mission, they talk not only about fighting drug runners on the open seas but about the $71 million they’ve spent to renovate and maintain the city’s airport, and the $6.5 million they inject each year into the local economy.

But the government of Ecuador has decided, and Washington has apparently agreed, that one of the most important foreign outposts in the United States’ war on drugs will close. The 450 U.S. Air Force personnel and contractors stationed at a military base that shares the airport’s runway will be leaving next year.

This decision reflects both the prevailing political climate here — standing up to the United States tends to be widely popular — and a new economic reality. With major projects underway in Manta by the Venezuelan government and a Hong Kong company, the U.S. dollars don’t amount to much.