obamaHAVANA, July 1 President Obama on Wednesday announced his plans to formally re-establish diplomatic relations with Cuba, declaring that the two nations were ready to reopen embassies in each other’s capitals and to start a “new chapter” of engagement after more than a half-century of estrangement.“Our nations are separated by only 90 miles, and there are deep bonds of family and friendship between our people, but there have been very real, profound differences between our governments, and sometimes we allow ourselves to be trapped by a certain way of doing things,” Mr. Obama said in the Rose Garden at the White House, taking note of the decades of hostility born of the Cold War that prompted the United States to isolate its neighbor to the south, a strategy he said had failed.

The diplomatic breakthrough is the most concrete progress to date in Mr. Obama’s push, announced in December after months of secret talks, for an official rapprochement with Cuba.

He also renewed calls on Wednesday for the lifting of a trade embargo with Cuba that has grown stricter over the years as Republicans in Congress, some of them Cuban-Americans, have pressed for a hard line against Havana.

“We don’t have to be imprisoned by the past,” the president said. “When something isn’t working, we can and should change.”

Mr. Obama said that Secretary of State John Kerry would travel to Havana this summer “to proudly raise the American flag over our embassy once more.”

Mr. Kerry, who is in Vienna for talks with Iranian officials on a potential nuclear accord, said that he would travel to Havana for the reopening of the United States Embassy. It would be the first visit to Cuba by a secretary of state since 1945, he said.

Acknowledging that the United States and Cuba continued to have “sharp differences” over human rights, Mr. Kerry said reopening the embassy would enable American officials to “engage the Cuban government more often and at a higher level.”

“This step has been long overdue,” Mr. Kerry added, declining to take questions.

Asked if the American diplomats in Cuba would have free access to talk to Cuban citizens, he said: “We’ll talk about all those details later.”

The United States already has a limited diplomatic outpost in Havana, called an interests section, in the same seven-story building on the Malecón waterfront that served as the embassy until 1961, the year President Dwight D. Eisenhower broke off diplomatic relations with Cuba in response to tensions with the revolutionary government of Fidel Castro.

Republicans who oppose the thaw with Cuba have vowed to block funding for an embassy and the confirmation of a new ambassador. But senior administration officials said on Wednesday that they did not believe they needed Congress to approve new money for the building and that they were in no rush to install a new ambassador to replace the career diplomat currently running the interests section.

The diplomat, Jeffrey DeLaurentis, was selected expressly because he is seen as someone who could serve as the acting ambassador pending a permanent appointment, one of the officials said on Wednesday, speaking on the condition of anonymity ahead of the release of details by the State Department.

Mr. DeLaurentis, who holds the rank of ambassador, has served at the United Nations, as a deputy assistant secretary of state and in Havana as the political-economic section chief.

Cuba has an interests section in a stately manor in the Adams Morgan section of Washington that could be upgraded. In May, Cuba announced that its banking services for that office had been restored, a precondition to reopening a full embassy. In recent weeks, Cuba also repaved the driveway, repainted the fence and erected a large flagpole on the front lawn to await the formal raising of its flag.

The official said that would happen on July 20, but it was not yet clear when Mr. Kerry would make the trip to Havana to cut the ribbon on the American Embassy there.