Venezuela's Hugo Chavez flew home on Friday after cancer surgery in Cuba, vowing to conquer the illness and win an October presidential election despite the need for radiation treatment.

"Who said the path was going to be easy?" said Chavez, 57, in an emotional speech to the nation on the runway. "I have promised I will live, and to this end I will give my all!"

The socialist president's return to Venezuelan soil after an absence of three weeks in Havana reasserts his leadership, calms anxiety among supporters and quells whispers of a succession struggle behind the scenes.

Yet little is known about what kind of cancer Chavez has or how serious it is. So big questions remain as to whether he is fit enough to campaign for an October 7 election that has turned into the biggest political fight of his 13-year rule.

Flying from Havana into Maiquetia international airport, on the Caribbean coast outside Caracas, Chavez smiled and hugged Cabinet members and relatives before giving a 30-minute address laced with religious and historical references.

"This new return is a song, a prayer, a commitment to God," Chavez said. The president appeared sure-footed, but at times his voice quivered and he lacked his typical exuberance.

"You can already smell the Bolivarian victory on October 7," he said, referring to his inspiration and Venezuelan independence hero Simon Bolivar. "They can't stop us!"

Chavez had said he would come home on Sunday, but in typically unpredictable fashion he caught officials by surprise by announcing his imminent return on Twitter. The highway to the airport was jammed with VIPs' motorcades, sirens blaring, as his top aides raced to be there when his plane landed.

Jubilant supporters quickly adopted the Twitter hashtag #ChavezVictorioso (Chavez Victorious).

In news that stunned Venezuelans accustomed to Chavez's energetic and dominant presence, Cuban doctors removed a baseball-sized cancerous tumor from his pelvis in June 2011.

Following that procedure, Chavez said he was 'completely cured'. But a recurrence of the disease dented his credibility about his health. Last month, Chavez flew to Cuba to have a second tumor removed.

RADIATION EFFECTS
Medical experts say the radiation treatment he faces could take a heavy physical toll. The cancer saga has eclipsed all other matters in South America's biggest oil exporter.

In Venezuela, where scant information has been released about Chavez's condition, everyone is speculating about what is happening behind the scenes.

Some theorise that Chavez invented his condition to win sympathy, while others predict that he has months to live.

Chavez has denied rumors the disease has spread.

On Friday, he said he was making a 'good recovery' but needed to apply a 'soldier's discipline' to slowing down his hectic lifestyle and following his medical routine.

Whatever his condition, the side effects of the radiation treatment will slow down the president's traditionally gregarious, on-the-street style, just as his 39-year-old opponent, Henrique Capriles, is gearing up his own campaign.

Capriles, a former state governor who won a strong mandate in an opposition primary election last month, is contrasting his energetic and youthful image with Chavez's convalescence.

On the campaign trail this week, Capriles walked for hours under the sun, visiting dozens of homes and shops to talk to Venezuelans, and enjoyed a game of basketball with locals.

"We are the new generation. We have energy and new ideas. We are the future, they are the past," Capriles told Reuters.

Opinion polls show Chavez, who has been in power since 1999, still has the edge over Capriles in voter enthusiasm, although roughly a third of the electorate is still undecided.

Though Capriles is a center-left politician who admires the Brazilian model of free-market economics combined with strong welfare policies, Chavez's camp depicts him as the epitome of what it calls the U.S.-backed, pro-rich "ultra right."

"We will continue bringing down the vile inheritance of capitalism," Chavez said in familiar flamboyant rhetoric.

One medical source close to the doctors treating Chavez said the Military Hospital in Caracas had been prepared to receive him. There was no official word, however, on whether Chavez would undergo radiation treatment at home or in Cuba.

A pro-opposition Venezuelan journalist, who has broken news on Chavez's condition, said Venezuelan, Brazilian and Spanish doctors involved in assessing him had disagreed with Cuban counterparts about where precisely the radiation should be applied to the president.