In Havana, women reading the state-run newspaper than ran Mr. Castro’s announcement.

HAVANA — Fidel Castro said Tuesday he would step down as the president of Cuba after a long illness, opening the way for his brother Raúl Castro or another member of his inner circle to become Cuba’s president when Parliament chooses a new leader this weekend.
if (acm.rc) acm.rc.write(); The announcement was made in a letter to the nation under Mr. Castro’s name, which was read on radio and television programs that many Cubans heard as they headed to work.
Under the Cuban Constitution, a newly chosen Parliament will choose a 31-member council of state on Sunday, which in turn will chose the next president. Though Cuban officials say the process is democratic, experts on Cuban politics say the decision on a successor remains in the hands of Fidel Castro, his brother and his inner circle, many of whom hold positions in the cabinet.
There seemed to be little if any outward reaction to the news, which many Cubans had been expecting for months. Schools remained open, garbage continued to be collected, and clusters of ordinary people waiting for buses or trucks to take them to work seemed as large and numerous as ever.
State-owned networks did not interrupt regular schedules, but read the announcement as part of the morning news, then returned to the usual mix of music and children’s broadcasting. Radio Rebelde, the radio service started by Mr. Castro in the mountains of the Sierra Maestra during the rebel uprising he led 50 years ago, broadcast popular music and a discussion of the roots of the Afro-Cuban sound, and mentioned his resignation only briefly during regularly scheduled newscasts, along with information about statements from the Venezuelan oil minister.
Despite the relative calm with which Tuesday morning’s announcement was received, the resignation signifies a monumental change on the island of some 11 million people. Mr. Castro’s decision to give up the presidency ends one of the longest tenures of a communist head of state, whose authority was among the most absolute.
In late July 2006, Mr. Castro, who is 81, handed over power temporarily to his brother, Raúl Castro, 76, and a few younger cabinet ministers, after he underwent emergency abdominal surgery. Despite many operations, he has never fully recovered, but has remained active in running government affairs from behind the scenes.
Now, just days before the National Assembly is to meet to select a new head of state, Mr. Castro has resigned permanently, and signaled his willingness to let a younger generation assume power, a proposition he first stated late last year. In the open letter to the Cuban people, he said his failing health made it impossible to return as president.
“I will not aspire to neither will I accept — I repeat I will not aspire to neither will I accept — the position of president of the Council of State and commander in chief,” he wrote in the letter, which was posted on the Web site of the state-run Granma newspaper in the early hours of Tuesday.
He added, “It would betray my conscience to occupy a responsibility that requires mobility and the total commitment that I am not in the physical condition to offer.”
President Bush, traveling in Rwanda on a tour of African nations, greeted the news by saying that the resignation should be the beginning of a democratic transition in Cuba leading to free elections. “The United States will help the people of Cuba realize the blessings of liberty,” he said.
Mr. Bush called for Cuba to release political prisoners and to begin building “institutions necessary for democracy that eventually will lead to free and fair elections.”
But the announcement puts Raúl Castro in the position to be anointed as the Cuban head of state when the National Assembly meets on Sunday, prolonging the power structure that has run the country since Mr. Castro became ill.
Mr. Castro’s announcement left unclear the roles that other high-level government ministers — including Vice President Carlos Lage Dávila, and Foreign Minister Felipe Pérez Roque — would play in the new government.
Mr. Castro also made it clear he was not fading into the sunset, but pledged to continue to be a force in Cuban politics through his writings, just as he had over the last year and a half. “I am not saying goodbye to you,” he wrote. “I only wish to fight as a soldier of ideas.”
That statement raised the possibility that little would change after Sunday’s vote, that Cuba would continue to be ruled in essence by two presidents, with Raúl Castro on stage while Fidel Castro lurked in the wings. At times over the last year and a half, the current government has seemed paralyzed when the two men disagree. In Washington, John D. Negroponte, deputy secretary of state, said it was unlikely that the United States would lift its trade embargo on Cuba, Reuters reported.
Mr. Castro has sent several signals in recent months that it was time for a younger generation to take the helm. For example, he said in December, “My primary duty is not to weld myself to offices, much less obstruct the path of younger people.”

Fidel Castro at a 2005 speech in Havana, Cuba.

Fidel Castro, left, with his brother, Raul, in 2006.

Fidel Castro addressed a crowd in Barbados in 1998.

In Tuesday’s letter, he expressed confidence that the country would be in good hands with a government composed of elements of “the old guard” and “others who were very young when the first stage of the revolution began.”
Mr. Castro said he had declined to step down earlier to avoid dealing a blow to the Cuban government before the people were ready for a traumatic change “in the middle of the battle” with the United States over control of the country’s future.
“To prepare the people for my absence, psychologically and politically, was my first obligation after so many years of struggle,” he said.
That strategy appeared to have been successful. After decades in which Mr. Castro seemed omnipresent, making endless speeches and appearing at rallies and ceremonies all over the island, he has not been seen in public since July 2006. No details of his illness or condition have ever been released. Many Cubans long ago accepted the fact that he must be seriously ill and would never be able to return to power.
“We are all born and we all die, and even if we wished that the commandante could be with us forever, it could not be,” said Eliana López, a state worker in the city of Matanzas who has lived nearly all of her 55 years with Mr. Castro as president. She said that his resignation was inevitable, as would be the total assumption of power by Raúl Castro. But she said she was convinced that although the change itself was monumental, the society built over the last 50 years would not undergo a drastic transformation.
“Under Raúl we will continue developing the same system that we’ve had over all these years,” Ms. Lopez said.
Mr. Castro seized power in January 1959 after waging a guerrilla war against the dictator Fulgencio Batista, promising to restore the Cuban Constitution and hold elections.
But he soon turned his back on those democratic ideals, embraced a totalitarian brand of communism and allied the island with the Soviet Union. He played a role in taking the world to the brink of nuclear war in the fall of 1962, when he allowed Russia to build missile-launching sites just 90 miles off the American shores. He weathered an American-backed invasion in 1961 and used Cuban troops to stir up revolutions in Africa and Latin America.
Those actions earned him the permanent enmity of Washington and led the United States to impose decades of economic sanctions that Mr. Castro and his followers maintain have crippled Cuba’s economy and kept their socialist experiment from succeeding completely.
The sanctions also proved handy to Mr. Castro politically. He cast every problem that Cuba faced as part of a larger struggle against the United States and blamed the “imperialists” to the north for the island’s abject poverty. A billboard on the so-called Monumental Highway leading to Havana declares that 70 percent of the Cuban population has lived under the embargo, which Cubans refer to as the blockade.
For good or ill, Mr. Castro is one of the most influential and controversial leaders to rise in Latin America since the wars of independence in the early 19th century, not only reshaping Cuban society, but providing inspiration for leftists across Latin America and in other parts of the world.
His record has been a mix of great social achievements and dismal economic performance that has mired most Cubans in poverty. He succeeded in providing universal health care and free education through college and made inroads in rooting out racism.
But he never broke the island’s dependence on commodities like sugar, tobacco and nickel, nor did he succeed in industrializing the nation so that Cuba could compete in the world market with durable goods.
Since the fall of the Soviet Union and the end of its aid to the island, Cuba has limped along economically, relying mostly on tourism and money sent home from exiles to get hard currency.
Yet Mr. Castro’s willingness to stand up to the United States and break free of American influence, even if it meant allying Cuba with another superpower, has been an inspiration to many Latin Americans, among them the new crop of left-leaning heads of state like Hugo Chávez of Venezuela, Evo Morales of Bolivia, and Luiz Inácio Lula da Silva of Brazil.
Though he never restored democracy or the Cuban Constitution as he had promised, and has ruled with absolute — and at times ruthless — power.
In the minds of many Latin Americans, he stood in stark contrast to right-wing dictators like the one he overthrew, who often put the interests of business leaders and the foreign policy goals of Washington above the interests of their poorest constituents. Whether Mr. Castro’s remaking of Cuban society will survive the current transition remains to be seen. Some experts note that Raúl Castro is more pragmatic and willing to admit mistakes than his brother. He has given signals he may try to follow the Chinese example of state-sponsored capitalism.
Others predict that, without Fidel Castro’s charismatic leadership, the government will have to make fundamental changes to the economy or face a rising tide of unrest among rank-and-file Cubans.