By Manuel Roig-Franzia
Washington Post Foreign Service

MEXICO CITY, Feb. 19 -- Fidel Castro announced early Tuesday morning that he is stepping down as Cuba's president, ending his half-century rule of the island nation.

"I am saying that I will neither aspire to nor accept, I repeat, I will neither aspire to nor accept the positions of President of the State Council and Commander in Chief," Castro, 81, said in a letter posted on the Web site of the state-run newspaper, Granma.

The announcement ends the formal reign of a man who, after seizing power in a 1959 revolution, not only outlasted nine U.S. presidents but his communist patrons in the former Soviet Union as well. Prior to the Soviet Union's collapse, support from the Kremlin sustained Cuba as a socialist outpost on the doorstep of the United States, and placed Castro and his country in the middle of events central to the Cold War, including the Bay of Pigs invasion and the Cuban missile crisis.

Those long-standing animosities colored Tuesday's announcement and U.S. reaction to it.

Castro said leaving office was a hard step for him given all that his "adversary" -- the United States -- had done over the years to try to get rid of him, including assassination plots.

President Bush, asked about the news in a public appearance during his trip to Africa, said: "The question really should be what does this mean for the people in Cuba. They are the ones who suffered under Fidel Castro."

Bush said he hoped this would be "the beginning of a democratic transition for the people of Cuba . . . An interesting debate will arise. Some will say let's promote stability. In the meantime, political prisoners will rot . . . This should be a transition to free and fair elections. And I mean free and fair. Not these elections that the Castro brothers rig."

Castro had temporarily handed over power to his younger brother, Raul Castro, in July 2006, after undergoing stomach surgery. He has kept a low profile since, but still officially holds the title of president and was widely believed to retain control over Cuba's government.

The ailing leader, who has a penchant for cryptic messages, mentioned in the letter posted Tuesday that he had hoped "to discharge my duties to my last breath. That's all I can offer."

Cuba's Council of State, a panel comprised of handpicked Castro allies, is scheduled to name the country's next president when it meets Sunday. In previous years, the selection was always a foregone conclusion, with the council picking Fidel Castro. The council is now widely expected to select Raul Castro, 76.

Fidel Castro made no mention of Cuba's future leadership in the letter. He had previously said that he hoped his brother would replace him. Vice President Carlos Lage and Foreign Minister Felipe Perez Roque are also considered top contenders to lead the nation.

Since taking power on an interim basis, Raul Castro, who is the head of Cuba's military, has repeatedly referred to his older brother as Cuba's "commander in chief."

"Raul, who is also minister of the Armed Forces on account of his own personal merits, and the other comrades of the Party and State leadership were unwilling to consider me out of public life despite my unstable health condition," Fidel Castro wrote. "It was an uncomfortable situation for me [vis-a-vis] an adversary which had done everything possible to get rid of me, and I felt reluctant to comply."

Cuban exiles and their supporters in the United States said they were skeptical that change will come soon with the Castro family still in charge.

"I have no hope that Raul Castro, who has been the older brother's enforcer, will be the agent of change that Cuba needs," U.S. Sen. Mel Martinez (R-Fla.), a Cuban native who has been staunchly anti-Castro, said in an interview on CNN. Nevertheless, "it is a good day for the Cuban people . . . At least we have one down and one to go."

Castro rose to power in the Cuban Revolution in 1959, an era when Socialist and Communist movements were gaining influence in many less developed countries. Alongside Ernesto "Che" Guevara, he became a revolutionary icon and drew followers from around the world.

Throughout his time in office, Castro clashed with the U.S. government, which backed a failed invasion of the island at the Bay of Pigs in 1961 and maintains a trade embargo against it.

Castro did not discuss the current state of his health in the letter, but did provide a narrative of his illness.

"In my necessary retreat, I was able to recover the full command of my mind as well as the possibility for much reading and meditation. I had enough physical strength to write for many hours, which I shared with the corresponding rehabilitation and recovery programs," he wrote. "Basic common sense indicated that such activity was within my reach. On the other hand, when referring to my health I was extremely careful to avoid raising expectations since I felt that an adverse ending would bring traumatic news to our people in the midst of the battle.

"I kept saying that my recovery 'was not without risks.' "

There were few people in the streets of Havana early on Tuesday after the announcement, according to a person in the capital who spoke by phone on condition of anonymity. There did not appear to be any unrest. Cuba has a small dissident movement among its 11 million people, but its leaders have not sought a change in the country's leadership since Castro's illness was announced.

Castro's announcement was posted on the Communist Party newspaper Web site before dawn on Tuesday. Access to the Internet is strictly limited in Cuba, and only a few elite politicians, military leaders and scientists have access in their offices or homes. The vast majority of Cubans can only access the Internet at state-run facilities, where they must pay an hourly fee and where many popular sites, such as Yahoo and Google, are blocked.

It is unclear what role, if any, Castro will play in governing Cuba now that he has officially stepped down. Many Cubans believe that he will be the real power in the nation -- regardless of titles -- as long as he is alive.

Raul Castro has pushed for reforms that would open the island's economy more to foreign investment, but Cuba experts say those reforms have been stymied by his brother. As head of the military, Raul Castro oversaw Cuba's tourism industry, a key source of revenue that helped revive Cuba's economy after the fall of the Soviet Union and the loss of subsidies from Moscow.

After the announcement on Tuesday, Trinidad Jimenez, Spain's secretary of state for Iberoamerica, suggested that economic reforms could be in the offing.

"This is a moment in which [Raul] can assume the process of reforms that he has spoken of with greater capacity, solidity and confidence and in which these reforms could start to materialize," Jim¿nez said, according to the Spanish news agency EFE.

Cuba struggles with a foundering economy that has left most residents living in poor conditions. Cuban officials blame their economic woes on the U.S. trade embargo, which they say makes it more expensive for them to import key items, such as rice -- a staple of the Cuban diet -- and cars.

Raul Castro has made numerous statements about trying to improve Cuba's inefficient agricultural system. During a speech last July in Camaguey, he criticized Cuban farmers for failing to cultivate land and announced plans to improve distribution of milk.

Castro's resignation is sure to resonate heavily in Florida, a bastion of anti-Castro sentiment where more than a million Cuban-Americans now live. Hundreds of thousands of supporters of the Fulgencio Batista regime fled to Florida and other parts of the United States after Castro's 1959 victory. Another wave of Cubans left the island during the 1980 Mariel boatlift when Castro allowed political opponents to emigrate. The exodus overwhelmed the city of Miami, which converted the famed Orange Bowl into a shelter.

Cubans continue to flee the island, in part because U.S. immigration policy gives them preferential status when seeking political asylum. Under the so-called "wet foot-dry foot" policy, Cubans captured at sea are generally denied entrance to the United States, while those who are caught on U.S. soil are generally allowed to stay.

The initial reaction to the news in Miami was cautious. Prominent exile leader Jos¿ Basulto said in a telephone interview that he didn't expect major changes. Basulto is the founder of the group Brothers to the Rescue, which aided rafters fleeing the island and dropped leaflets condemning Castro in Havana in the 1990s. The Cuban government has accused the group of being involved in terrorist attacks on the island, an accusation denied by Basulto.

Basulto has been trying to persuade the U.S. government to back his effort to bring criminal charges against Raul Castro for the downing of two Brothers to the Rescue airplanes off of Havana in 1996.

On Tuesday, Basulto said: "If the United States truly wants change in Cuba, they will help us with this. If Raul Castro is charged, there cannot be a legal succession of power in Cuba."

Janisset Rivero, the executive director of Cuban Democratic Directorate, a group that works with dissidents in Cuba, told CNN that Fidel Castro's announcement "doesn't mean any change to the system. It doesn't mean there will be freedom for the Cubans. One big dictator is replacing the other."

Exiles in the blogosphere, meanwhile, scoffed at the idea that this would bring meaningful change.

"We are supposed to sigh and take a breath of relief. Not us," one anti-Castro blogger wrote early Tuesday. "Be alert, the Cuban people is not free. The tyranny apparatus is in place, Castro and Castroism are still there. No changes."