HAVANA — Fidel Castro, who has wielded absolute power in Cuba for nearly half a century, remained out of sight yesterday after undergoing intestinal surgery and temporarily turning over power to his brother Raul Castro.

The surprise announcement that Mr. Castro had been operated on to repair a “sharp intestinal crisis with sustained bleeding” stunned Cubans on the island and in exile, and the event marked the first time that Mr. Castro, two weeks away from his 80th birthday, had relinquished power in 47 years of rule.

On this island 90 miles south of Florida, people went about their business as normal on the streets of Havana early yesterday, standing in line for buses to school and work and jogging along the city’s famous Malecon seawall.

Some government work centers called workers to participate in outdoor political gatherings later yesterday to express their support for Fidel Castro.

The news came Monday night in a statement read on state television by his secretary, Carlos Valenciaga. The message said Mr. Castro’s condition was apparently due to stress from a heavy work schedule during recent trips to Argentina and eastern Cuba. He did not appear on the broadcast but said in the statement that he was temporarily handing over leadership of the Communist Party to his younger brother.

Mr. Castro took control of Cuba in 1959, resisted repeated American attempts to oust him, and survived communism’s demise elsewhere.

The defense minister who turned 75 in June, Raul Castro also did not appear on television and made no statement on his own. For decades the constitutional successor to his brother, Raul Castro has assumed a more public profile in recent weeks.

Fidel Castro last appeared in public last Wednesday as he marked the 53rd anniversary of his July 26 barracks assault that launched the revolution.The Cuban leader seemed thinner than usual and somewhat weary during a pair of long speeches in eastern Cuba.

A White House spokesman, Peter Watkins, said American authorities were monitoring the situation: “We can’t speculate on Castro’s health, but we continue to work for the day of Cuba’s freedom.”

On Monday, before Mr. Castro’s illness was announced, President Bush was in Miami and spoke of the island’s future.

“If Fidel Castro were to move on because of natural causes, we’ve got a plan in place to help the people of Cuba understand there’s a better way than the system in which they’ve been living under,” he told WAQI-AM Radio Mambi. “No one knows when Fidel Castro will move on. In my judgment, that’s the work of the Almighty.”

Three weeks ago, an American presidential commission called for an $80 million program to bolster nongovernmental groups in Cuba for the purpose of hastening an end to the country’s communist system.

Fidel Castro seemed optimistic about his recovery, asking that celebrations scheduled for his 80th birthday on August 13 be postponed until December 2, the 50th anniversary of Cuba’s Revolutionary Armed Forces.

With Havana’s streets calm, an electronic news ticker at the American diplomatic mission provided the only clue that something dramatic had occurred inside Cuba’s government: “All Cubans, including those under the dictatorship, can count on our help and support. We respect the wishes of all Cubans.”

Across the Florida straits in Miami, exiles waved Cuban flags on Little Havana’s Calle Ocho, shouting “Cuba! Cuba! Cuba!” as drivers honked their horns. Over nearly five decades, hundreds of thousands of Cubans have fled Mr. Castro’s rule, many of them settling in Miami.

[Fidel Castro said his health was stable after surgery and he was in good spirits yesterday, the AP reported. A Castro statement read on state television began with Mr. Castro saying, “I can not make up positive news.” But he said his health was “stable,” and “as for my spirits, I feel perfectly fine.”

Mr. Castro expressed his gratitude for all the good wishes he’s received.]