CAMAGUEY, Cuba — Interim leader Raul Castro led tens of thousands of loyalists today in celebrations of Cuba's revolution, filling in for his ailing brother Fidel at a key event as the provisional government took on an air of permanence.

Cuba's 76-year-old acting president and defense minister — not his elder brother — arrived for the Revolution Day festivities in Camaguey, a provincial capital of narrow colonial streets and daily afternoon downpours southeast of Havana. He was to address the crowd later.

Fidel, who turns 81 next month, has for decades given speeches lasting hours to mark Cuba's top holiday. In 2006, he addressed crowds in two separate cities on Revolution Day.

But he has not been seen in public since, apparently still too sick to appear in person after announcing on July 31, 2006, that emergency intestinal surgery was forcing him to step aside in favor of Raul.

He has begun penning essays dubbed "Reflections of the Commander in Chief" every few days, but appears to be in little hurry to return to power.

"I am certain Fidel is recovering, but there's no problem because we have Raul," said Candida Alvarez, a 76-year-old retiree who hung a string of paper red, white and blue Cuban flags from the front door of her wooden home near Camaguey's historic center.

Alvarez, who works with neighborhood communist officials to mediate disputes between residents, said "Fidel will always be the boss, but now Raul is the boss too."

"He's been there for a year and has gained popularity, earned the warmth of the people," she said.

Raul Castro has said would be willing to discuss improving relations with Washington.