The two countries exchanged ambassadors again last year, but things have not always gone smoothly for the new American envoy, Adam E. Namm.

Last month, Mr. Correa, who has warred continually with the news media in his country, reacted angrily after Mr. Namm attended an event in favor of freedom of expression that was organized by the National Journalists Union. Mr. Correa called Mr. Namm a meddler and warned him to behave. The foreign minister, Ricardo Patiño, said darkly that the next time he might get more than just a warning.

The last sustained high-level contact between the two countries may have come in 2010, when Secretary of State Hillary Rodham Clinton visited Ecuador. During that visit, Mr. Correa told her, “We’re not anti-American; we love America,” and he described his years as a student at the University of Illinois as the happiest of his life.

But Mrs. Clinton pressed him on his government’s crackdown on the news media, and when an Ecuadorean journalist challenged him about his policies at a news conference, the president rebuked him while Mrs. Clinton watched stone-faced.

The most likely casualty of sheltering Mr. Snowden would be the trade preferences, which have been in place since the early 1990s. Originally designed for several Andean nations, Ecuador is the last remaining recipient. But the preferences, which applied to about $429 million in non-oil exports last year, expire at the end of July unless they are renewed by Congress.

That renewal was already in doubt, not least of all, officials said, because the oil giant Chevron has been lobbying hard against Ecuador. The campaign is part of Chevron’s response to an $18 billion penalty against the company ordered by an Ecuadorean court in a case over environmental damages related to oil drilling in the Amazon.

But Ecuador has begun its own campaign to keep the preferences, including a Web site called Keep Trade Going, that urges Americans to contact their legislators to ask them to vote in favor of the pact.