By Andrew Cawthorne
CARACAS (Reuters) - Venezuelan President Hugo Chavez said on Tuesday he would undergo a fourth round of chemotherapy soon but expected to be fully fit by the end of the year in time for a presidential election campaign.
The 57-year-old socialist leader has led South America's top oil exporter since 1999 and changed the constitution to allow indefinite re-election. But his hopes for a lengthy rule were thrown into doubt by a cancer diagnosis this year.
Phoning into an early morning state TV program, Chavez said he had recovered from a throat infection that kept him out of public view in recent days and showed his vulnerability to infections during the cancer treatment.
"I have faith, my recovery is going well," he said.
Chavez -- who has lost hair during the first three sessions of chemotherapy, prompting supporters to shave heads in solidarity -- said he will have a fourth round in coming days.
"After this chemotherapy, the last one God-willing, I will undoubtedly start physical exercise," said Chavez, who has restricted his famously demanding work schedule during his treatment.
Doctors plan a full evaluation in October to check there are no more malignant cells, the president added.
Chavez targets being fit again for a regional summit Venezuela plans to host on December 2. "By that date, I should be fully recovered for an activity like that," he said.
Chavez had a large, cancerous tumor removed in June, but has not given full details. Experts surmise the operation -- and ongoing treatment -- was around the colon or pelvis areas.
Despite doubt among political analysts and his opponents, Chavez said he should be able to run a vigorous campaign ahead of the 2012 presidential election vote, and reaffirmed his ambition to rule for at least two more six-year terms.
Opinion polls show a small sympathy boost for Chavez since he announced his cancer treatment, with various recent surveys putting his approval ratings at more than 50 percent. That is lower than some other moments of his rule, but still a formidable level for a man in his 13th year in power.
In the coming election campaign, "Chavez will be the same, and now even renewed, refreshed, recharged," he said.
Also refreshed, however, is Venezuela's opposition movement, which has finally united under an umbrella group after years of contributing to its own failures by bickering and policy differences among parties and leaders.
The opposition has scheduled primaries in February to pick a unity candidate, with a youthful state governor, Henrique Capriles Radonski, the favorite to win that.
One big, unknown factor in Venezuela's political scenario is the date of the election.
Traditionally held in December, there is speculation the date may be brought forward to try and catch the opposition off-guard. That, however, would give Chavez less time to recover from his cancer treatment.
Venezuela's National Election Board, which is close to the government, may announce the date this week.
(Additional reporting by Marianna Parraga; Editing by Eric Beech)