WASHINGTON — The United States and Cuba will announce an agreement on Wednesday to reopen embassies in each other’s capitals, formally restoring diplomatic relations more than a half-century after they were ruptured, according to administration officials.

The agreement represents the most tangible outcome to date of President Obama’s decision to reach out to the island nation and end its decades of isolation. Mr. Obama declared in December that he wanted to resume ties with Havana, and the two sides have spent the last six months in painstaking negotiations to work out details of the new embassies.

Mr. Obama will announce plans to reopen the embassies in the Rose Garden on Wednesday morning. Secretary of State John Kerry will also discuss the plans in Vienna, where he is negotiating a nuclear agreement with Iran, according to the officials, who insisted on anonymity in advance of the formal announcement. Mr. Kerry plans to travel to Havana for the actual opening of the embassy on July 22.

President Dwight D. Eisenhower broke off diplomatic relations with Cuba in January 1961 just before leaving office in response to increased tensions with the revolutionary government of Fidel Castro. A trade embargo imposed by Mr. Eisenhower was then toughened by his successors, and the two neighbors have spent more than 50 years at odds.