Castro remains a member of parliament and is likely to be elected to the 31-member Council of State on Sunday, though he will no longer be its president. Raul Castro's wife, Vilma Espin, maintained her council seat until her death last year even though she was too sick to attend meetings for many months.

Castro also retains his powerful post as first secretary of Cuba's Communist Party. The party leadership posts generally are renewed at party congresses, and the last one was held in 1997.

The resignation opens the path for Raul Castro's succession to the presidency, and the full autonomy he has lacked in leading a caretaker government. The younger Castro has raised expectations among Cubans for modest economic and other reforms, stating last year that the country requires unspecified "structural changes" and acknowledging that government wages that average about $19 a month do not satisfy basic needs.

As first vice president of Cuba's Council of State, Raul Castro was his brother's constitutionally designated successor and appears to be a shoo-in for the presidential post when the council meets Sunday. More uncertain is who will be chosen as Raul's new successor, although 56-year-old council Vice President Carlos Lage, who is Cuba's de facto prime minister, is a strong possibility.

"Raul is also old," allowed Isabel, a 61-year-old Havana street sweeper, who listened to Castro's message being read on state radio with other fellow workers. "As a Cuban, I am thinking that Carlos Lage, or (Foreign Minister) Felipe Perez Roque, or another younger person with new eyes" could follow the younger Castro brother, she added.

Bush, traveling in Rwanda, pledged to "help the people of Cuba realize the blessings of liberty."

"The international community should work with the Cuban people to begin to build institutions that are necessary for democracy," he said. "Eventually, this transition ought to lead to free and fair elections — and I mean free, and I mean fair — not these kind of staged elections that the Castro brothers try to foist off as true democracy."

The United States built a detailed plan in 2005 for American assistance to ensure a democratic transition on the island of 11.2 million people after Castro's death. But Cuban officials have insisted that the island's socialist political and economic systems will outlive Castro.

"The adversary to be defeated is extremely strong," Castro wrote Tuesday. "However, we have been able to keep it at bay for half a century."