The 80-year-old communist leader was not watching from his usual perch atop a viewing platform and has not been seen in public since emergency intestinal surgery forced him to step down temporarily nine months ago.

Castro has attended the annual International Workers' Day march for decades. Cuban officials had refused to speculate on whether he would use this year's event to make his first public appearance since undergoing surgery and temporarily ceding his duties to his 75-year-old brother.

One of Castro's main allies, Venezuelan President Hugo Chavez, said Sunday that the Cuban leader is once again "in charge," but he declined to comment on statements by Bolivia's leftist leader that Castro could appear in public on May 1. Full story

There was no word on Cuban state television's nightly newscast. Castro issued the latest in a new series of communiques, calling for a revolution in energy production, but gave no hint of whether he would make a May Day appearance.

He reiterated his opposition to U.S. plans to use food crops to produce ethanol for cars, predicting that American fuel needs would be provided with the labor of the world's impoverished sugar cane workers.

"Tomorrow the first of May is a good day to carry these reflections to the workers and all of the poor people of the world," Castro wrote in the communique dated Monday evening.

A wooden platform on the broad Plaza of the Revolution was decorated for the May Day event with huge banners bearing portraits of the island's communist heroes. But the urgent need by many to see the man who ruled this country for 47 straight years seems to have faded in recent months as life has continued normally under the leadership of Castro's younger brother Raul, the defense minister.

Occasional government photographs and videos of the elder Castro have assured Cubans he is still alive and recovering, appearing stronger and more robust in the most recent images.

There will be smaller marches in cities around the island, with the government expecting several million of the nation's 11 million people to participate. Those gathered also will protest the recent decision to free on bond anti-communist militant Luis Posada Carriles, pending his trial on U.S. immigration charges. Havana accuses the Cuban-born Posada of orchestrating a 1976 airliner bombing that killed 73 people -- a charge he denies.

Castro has met in recent weeks with Colombian writer and Nobel laureate Gabriel Garcia Marquez and a top Chinese Communist Party leader, and has penned four editorials, including the one issued Monday evening.