“There is no such thing as a country that is simply a transit country, for the very simple reason that the drug trafficking organization first pays its network in product, not in cash, and is constantly looking to build a greater market,” Mr. Brownfield said. “Regardless of the name of the country, eventually the transit country becomes a major consumer nation, and at that point they have a more serious problem.”

The United Nations says that cocaine smuggling and consumption in West Africa have soared in recent years, contributing to instability in places like Guinea-Bissau. Several years ago, a South American drug gang tried to bribe the son of the Liberian president to allow it to use the country for smuggling. Instead, he cooperated with the D.E.A., and the case resulted in convictions in the United States.

Even more ominous, according to American officials, was a case in which a militant group called Al Qaeda in the Islamic Maghreb offered three of its operatives to help ship tons of cocaine through North Africa into Europe — all to raise money to finance terrorist attacks. The case ended this past March with conviction and sentencing in federal court in New York.

American counternarcotics assistance for West Africa has totaled about $50 million for each of the past two years — up from just $7.5 million in 2009, according to the State Department. The D.E.A. also is opening its first country office in Senegal, officials said, and the Pentagon has worked with Cape Verde to establish a regional center to detect drug-smuggling ships.

While the agency has not sponsored units in West Africa before, it has long worked with similar teams — which are given training, equipment and pay while being subjected to rigorous drug and polygraph testing — in countries around the world whose security forces are plagued by corruption, including the Dominican Republic, El Salvador, Guatemala and Panama.

It is routine for D.E.A. agents who are assigned to mentor the specially trained and screened units to accompany them on raids, but it has been unusual for Americans to kill suspects. Several former agents said the recent cases in Honduras suggested that the D.E.A. had been at the vanguard of the operations there rather than merely serving as advisers in the background.

By contrast, the effort in West Africa is still at the beginning stages, officials say. But the problems there are the same — and growing. Officials described one instance in which a methamphetamine lab was discovered in Africa, with documents suggesting that it had been set up by a Mexican trafficking organization. William F. Wechsler, the Pentagon’s top counternarcotics officer, said that observing drug traffickers’ advances into West Africa, and the response from American and local authorities, was like watching a rerun of the drug war in this hemisphere in years past.

“West Africa is now facing a situation analogous to the Caribbean in the 1980s, where small, developing, vulnerable countries along major drug-trafficking routes toward rich consumers are vastly under-resourced to deal with the wave of dirty money coming their way,” he said.