HAVANA — Fidel Castro called the building a “nest of spies,” routinely marshaling tens of thousands of people to protest at its doorstep. His government even made a television mini-series with what it called images of American diplomats lurking in a forest nearby, dropping off suspicious bags and marking benches in acts of espionage.
President George W. Bush took swipes of his own, installing a Times Square-style ticker on the building’s side to flash news and political statements. The move so enraged Cuban officials that they erected a thicket of 138 black flags on towering poles to block the sign.
Now the building, the American government’s main outpost in Cuba, for decades a hulking symbol of the tensions between the two countries, is supposed to become something else: a full-fledged embassy operating in the open for the first time in more than five decades.
Officially, the six-story embassy, in a choice spot along Havana’s seaside highway, was closed after President Dwight D. Eisenhower broke ties with Cuba in 1961. Yet it has hardly been dormant. Since 1977, the United States has run it as an “interests section” to process visas, hold cultural events and keep some communication flowing between the two estranged neighbors.
The president discussed the move to normalize relations with Cuba during his State of the Union address.
But all the while, it has also served as the staging ground for an on-again, off-again game of tit for tat — and spy versus spy.
“We were the closest of enemies,” Wayne S. Smith, who was the first chief of the mission in 1977, once remarked.
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Still, despite the periods of animosity, a couple of interest section chiefs got to spend time with Fidel Castro before he turned over power to his brother, Raúl, who has not been known to see American officials in recent times.
Mr. Smith recalled that as he was about to leave Cuba, he was summoned to a beach house. Fidel Castro was holding a farewell cookout for him.
What they discussed, he prefers to keep classified.
Because of an editing error, an earlier version of this article misstated the year that the American outpost began to be used as an “interests section.” It was 1977, not 1997. The same error appeared in an earlier version of a picture caption with this article.
Mark Mazzetti contributed reporting from Washington.
A version of this article appears in print on January 21, 2015, on page A1 of the New York edition with the headline: U.S. Outpost in Cuba to Step Out of Shadows. Order Reprints| Today’s Paper|Subscribe
