* Crescendo of speculation over president's condition
* Cancer threatening to end his 14-year-old rule
* Officials say Chavez "fighting" for life (Adds information minister, details)
By Andrew Cawthorne
CARACAS, March 1 (Reuters) - Senior aides and relatives of Venezuela's Hugo Chavez countered on Friday a crescendo of rumors that the socialist president may be dead from cancer, saying he was still battling for his life.
"There he is, continuing his fight, his battle, and we are sure of victory!" his brother Adan Chavez, the governor of Barinas state, told cheering supporters during an event.
Speculation about Chavez, 58, has reached fever pitch this week, fed in part by assertions from Panama's former ambassador to the Organization of American States (OAS), Guillermo Cochez, that the Venezuelan leader had died.
"The launching of absurd and bizarre rumors by the right wing simply discredits them and isolates them further from the people," Chavez's son-in-law Jorge Arreaza, who is also Venezuela's science minister, said via Twitter.
Apart from one set of photographs showing Chavez in a hospital bed, he has not been seen or heard from in public since Dec. 11 cancer surgery in Cuba, his fourth such operation. He returned to a military hospital in Caracas last week.
Vice President Nicolas Maduro, now Venezuela's de facto leader and Chavez's preferred successor, has also said several times during the week that the president was fighting for life and urged Venezuelans to be patient with the situation.
Opposition politicians accuse the government of being deceitful about the president's condition, and compare the secrecy over his medical details with the transparency of other Latin American leaders who have suffered cancer.
Cochez, who said relatives had taken Chavez off life support several days ago after he had been in a vegetative state since the end of December, challenged the Venezuelan government to prove him wrong by showing the president in public.
Across the South American nation of 29 million people, Venezuelans are extremely anxious, speculating endlessly about Chavez's condition and wondering what the potential end of his 14-year rule might mean for them.
Adding to the tension, several dozen students have chained themselves up in public, demanding to see the president.
Should Chavez die or step down, an election would be held within 30 days, probably pitting Maduro against opposition leader and state governor Henrique Capriles for leadership of the OPEC member nation with the world's biggest oil reserves.
The stakes are high for the region, too, given Chavez's role as Washington's main irritant in Latin America and the aid his government gives leftist governments from Cuba to Bolivia.
Amid the flurry of rumors, Spain's ABC newspaper said on Friday that Chavez had been taken to a presidential retreat on La Orchila island in the Caribbean off Venezuela's coast with his closest family to face the "final stages" of cancer.
Venezuelan officials have frequently lambasted ABC as being part of an "ultra-right" conspiracy spreading lies about Chavez.
"There's a psychological operation underway to upset the Venezuelan people," complained Information Minister Ernesto Villegas on Friday, condemning the "frightful" versions about Chavez's state flying around the Internet.
"Leave the Venezuelan people in peace," he added. "President Chavez is in his process of recovery. His family is with him ... The revolution continues."
In the latest of short updates on Chavez's health, the government said last week his breathing difficulties had grown worse, and he was using a tracheal tube.
The respiratory problem was a complication from a complicated, six-hour operation in December for a cancer first detected in Chavez's pelvic region in June 2011.
Remarkably, two opinion polls this week showed that a majority of Venezuelans - 60 percent in one survey, 57 percent in another - believe Chavez will be cured.
"The prolonged absence of the president and his critical situation have not turned into massive pessimism," said one of the pollsters, Luis Vicente Leon.
Chavez's millions of passionate supporters, who love his down-to-earth style and welfare policies, are struggling to imagine a Venezuela without him.
"Of course, he's coming back, back to government," said Jose Urbina, 47, buying photos of Chavez at a pro-government rally. "I want to remember him, I want to put them in my house." (Additional reporting by Girish Gupta; Editing by Daniel Wallis, Vicki Allen and Eric Walsh)