* President has not been seen in a month
* Chavez missed Jan. 10 inauguration ceremony
* Leaders of Argentina, Peru also in Havana
By Daniel Wallis and Diego Ore
CARACAS, Jan 11 (Reuters) - Venezuela's Vice President Nicolas Maduro will fly to Cuba on Friday to visit cancer-stricken Hugo Chavez, a month after the socialist leader underwent his fourth operation in 18 months.
The 58-year-old president has neither been seen nor heard from since the surgery, and he has suffered multiple post-operative complications including a severe lung infection.
He missed his own inauguration on Thursday, but the Supreme Court said he could be sworn in later - in theory meaning he could remain in office for weeks or months from a Havana hospital. There has been no firm evidence he is conscious.
"I'm going to give our commander-president the good news about how the people are working, making revolution with courage, discipline and enthusiasm," Maduro said in a televised broadcast.
Argentine President Cristina Fernandez, a friend and ally of Venezuela's socialist leader, arrived in Cuba on Friday and said she planned to take Chavez a Bible.
Talking to reporters at Havana's landmark Hotel Nacional, she said she would have lunch with President Raul Castro and his older brother and predecessor, Fidel Castro, and then expected to meet members of Chavez's family.
"This is not a visit for making comments or giving interviews but simply of solidarity and fellowship with someone who is a friend," Fernandez said.
Peru's President Ollanta Humala - whom Maduro called another "comrade in arms" of the Venezuelan president - also visited the Cuban capital on Friday.
Humala said he was in Havana to sign various accords but that he would also inquire about Chavez's condition.
"We all wish ... a quick improvement," the Peruvian leader said on his arrival at the airport.
SILENCE FROM CHAVEZ
Unlike after Chavez's previous cancer operations in Cuba, the government has published no photos or video of the former soldier's recovery. Neither has he made any of his normally frequent phone calls back home to Venezuelan state television.
While Maduro has said he spoke to Chavez by telephone and in person during a previous visit to Havana, his comment on Dec. 24 that the president had been up walking and doing exercises was met with derision from many in the South American country.
Perhaps more than anything, the silence from the normally garrulous leader famous for his lengthy diatribes has led many to believe his 14 years in power may be coming to an end.
In his absence, government officials were forced to postpone a ceremony on Thursday to swear him in for the new six-year term that he won at a presidential election in October.
A clutch of Latin American and Caribbean leaders attended a rally that went ahead in Caracas regardless, where thousands of red-shirted loyalists held aloft copies of the constitution and were symbolically sworn-in in Chavez's place.
His condition is a top concern of officials in Cuba and other allied nations whose leftist governments have long benefited from years of Chavez's oil-fueled generosity.
Maduro, a former bus driver and union leader who shares his boss's radical views, is in day-to-day charge of the government until there is clarity over whether the president will return.
He has sought to imitate Chavez's bombastic rhetoric in speeches but struggles to emulate the folksy charisma of the president, who grew up in humble surroundings and became one of the world's best-known heads of state.
Venezuela's opposition leaders are furious at what they see as a Cuban-inspired manipulation of the constitution by Maduro and other top "Chavista" figures aimed at preventing the naming of a caretaker president due to Chavez's absence.
Should Chavez die or have to step down, a new election would be called and would likely pit Maduro against opposition leader Henrique Capriles, the 40-year-old governor of Miranda state.