By Andrew Cawthorne
CARACAS (Reuters) - Venezuela's ailing socialist leader, Hugo Chavez, was authorized by parliament on Thursday to fly to Cuba for as long as needed to have more cancer surgery that has shaken the country ahead of a presidential election.
"I will return as always, with more energy, more enthusiasm, more joy and determination to take my place in the vanguard," Chavez said in a letter requesting permission to travel abroad for more than five days, as required by the constitution.
The "indefinite permission" was quickly approved by the National Assembly, where Chavez has a majority, and raised the specter of another possible lengthy absence after he spent weeks being treated in Havana last year.
Chavez, 57, who needs surgery on a lesion in the same place a cancerous pelvic tumor was removed last year, may leave as soon as Friday. The new lesion was discovered during a weekend trip to Cuba last year. Chavez is a friend of Cuba's former president, Fidel Castro, and is guaranteed discreet treatment there.
"I am completely sure we will win this new battle," Chavez wrote in typically confident language.
Opposition politicians - who see the October 7 presidential vote as their best chance to end Chavez's 13-year rule - have called for him to name a temporary replacement. But that looks unlikely seeing as last year he ran affairs of state from his hospital bed.
"You cannot govern from anywhere that is not in national territory," opposition legislator Alfonso Marquina said. "We demand that the constitution be respected."
In October Chavez had declared himself cured but his health downturn has thrown his re-election campaign into uncertainty, with questions also being asked about his capacity to rule for another six-year term.
Since storming to power in a 1998 election, the sports-loving former soldier has thrived on an image of physical strength and is clearly shaken by his health problems.
While his latest operation is likely to evoke sympathy, analysts say that could be offset by concerns over his fitness to rule. By contrast, opposition candidate Henrique Capriles, 39, projects an image of youth and energy.
"On one hand, it seems unlikely that Venezuelans want to vote for a weak president," said Gabriel Sanchez Zinny, a Latin American expert with U.S-based Blue Star Strategies consultancy.
"On the other hand, it is possible that he is using his condition to portray himself as a victim, thereby attempting to garner sympathy from voters."
Chavez, who has dominated Venezuela since taking office in 1999 and whose fierce anti-U.S. rhetoric has turned him into one of the world's best-known leaders, said the 2-centimeter lesion is probably malignant.
Cancer experts say that sounds ominous, although Chavez has presented the imminent operation as straightforward.
The government has given no more medical details, meaning Venezuela's rumor mill is in overdrive, with theories ranging from his imminent death to the whole thing being a hoax.
Prominent pro-opposition journalist Nelson Bocaranda, who broke the news of Chavez's latest condition, said on Thursday Chavez was paying the price for ignoring doctor's orders to rest. In his latest column on Chavez's health, Bocaranda said he may have metastasis - although the president denied the cancer had spread.
"It is not an encouraging panorama for the man who ignored recommendations with the sole objective of winning the presidency in October," he said.
Venezuela's widely traded bonds, buoyed by market hopes for a more business-friendly government in the South American OPEC nation, have jumped in recent days.
On Thursday, the Global 2027 bond rose to its highest price in almost two years, climbing 1.875 percent to bid at 83.313.
Before the latest cancer news, polls gave Chavez an edge over Capriles, the governor of Miranda state, for October.
While critics highlight Chavez's authoritarian tendencies to portray him as a dictator bent on imposing Cuban-style communism on Venezuela, he remains immensely popular among the poor, who have benefited from his big spending on welfare policies.
(Additional reporting by Diego Ore and Marianna Parraga; Editing by Daniel Wallis and Bill Trott)