By Hugh Bronstein

CARACAS (Reuters) - Just months ago, it was the issue dominating Venezuela and its presidential campaign. Now Hugo Chavez's bout with cancer is barely mentioned as his October 7 re-election bid approaches.

Once-frenetic rumors about Chavez's health have cooled to almost nothing while voters prepare to decide who will lead Venezuela - and control its vast oil reserves - for the next six years.

Chavez, a socialist firebrand known for lambasting the U.S. "empire," faces market-friendly challenger Henrique Capriles, a 40-year-old lawyer and state governor who has vowed to end the seizure of private businesses and create jobs by attracting private investment.

Chavez wants to deepen his self-styled revolution and says he is cured of cancer after three operations in Cuba since June 2011. But details of the cancer involved and the exact location of the tumors have remained secret to all but a few confidants, including Chavez's mentor, former Cuban leader Fidel Castro.

Chavez's health fell off the map as an electoral issue when it became clear in July that the 58-year-old ex-paratrooper was getting stronger and would almost certainly live at least until the October vote.

"He stopped talking about it and the opposition decided it would be better to win with a message of change and recovery than by talking about Chavez's health," said businessman Rafael Cubillan, 71, sipping a drink in a Caracas cafe.

"It would be better if voters had all the facts before they go to the polls," he added. "But Chavez comes from the vertical command structure of the military. He tells his troops only what they need to know to help him get the result he wants."

The president has ramped up his campaign schedule and appears healthy, if a bit bloated. His hair has grown back after chemotherapy caused him to go bald last year.

He is still not walking the streets much, preferring to appear on stage or on the top of a vehicle dubbed the "Chavez-mobile" in highly scripted rallies: a far cry from the coffee-swilling, barely sleeping, all-energy campaigner of the past.

But he is seen in public several times a day, kissing babies at campaign events and bursting into song during speeches that can run for hours, and are just as combative as ever.

'IN REMISSION'

Everyone, from voters in the Caracas slums to bondholders and executives of foreign oil companies drooling to tap into Venezuela's oceanic crude reserves, has been left in the dark as to Chavez's exact condition.

A Venezuelan medical source with knowledge of his treatment said the president had been declared "in remission" by his Cuban doctors after several rounds of radiotherapy.

"They keep giving him a lot of medication to accelerate his physical recovery, which is reflected in his mood and appearance," the source said.

Doctors say Chavez's declaration of full recovery is medically unsound, given that a couple of years would have to pass without a recurrence for it to be clear he was cured.

Many Venezuelan doctors suspect Chavez has been using steroids and other treatments to look and feel fitter and help him keep up the pace of his campaign. They say this could create more health problems if he pushes himself too hard.

If Chavez wins reelection, any sign of frailty would likely jump-start speculation about his health and succession scenarios, putting markets on edge.

Venezuela has the world's biggest oil reserves and its high-yielding sovereign bonds are some of the most heavily traded in the market. Its relationship with Colombia, with which it shares a long border rife with drug trafficking, is also key to the stability of the Andean region.

Chavez enjoyed a sympathy bounce in opinion polls when the issue of his health first came up, but with the election now less than three weeks away, he clearly feels that suggestions of physical frailty are not the way to win votes.

Asked about his health last week, Chavez brushed off the question, saying simply: "I'm fine, as you can see by looking at me." By contrast, he spent hours answering other questions, reflecting his desire to take attention away from the cancer.

Most of the best-known opinion polls put Chavez ahead, but voter surveys are notoriously controversial and divergent in Venezuela, and Capriles' numbers have been creeping up. A major pollster last week put him just ahead of Chavez.

Capriles is not touching the health question, other than to wish Chavez a speedy recovery, leaving investors and many voters hoping someone will leak the facts about the president's health.

"Where's the Julian Assange of Venezuela when you need him?" said Stephen Donehoo, a Latin American expert at Washington-based business consultancy McLarty Associates. Assange burst into the headlines in 2010 as the head of WikiLeaks, which caused a furor by publishing secret U.S. diplomatic cables.

"Venezuelans should have the right to know the state of health of the person who wants to lead them for the next six years, particularly with so much at stake," Donehoo said.

(Additional reporting by Marianna Parraga; Editing by Daniel Wallis, Kieran Murray and David Brunnstrom)