Teenage girls scream, fishermen fallen on hard times thrust tatty documents forward, and crowds swallow Henrique Capriles' fist-pumping figure at chaotic stops along the Caribbean coast.

Venezuela's young opposition front-runner is all energy as he criss-crosses the South American nation ahead of a February 12 primary likely to make him President Hugo Chavez's challenger in this year's presidential election.

Though he has four rivals in the Democratic Unity coalition primary, the 39-year-old state governor is well ahead in polls and already looking forward to matching the socialist president's own pumped-up style in an October 7 duel.

What you see here is like 1998 when Chavez ran for the first time. He didn't have the machinery, but he did have the people, Capriles told Reuters on a recent campaign tour, sweating from the heat at the back of a bus before his next walkabout in Cumana town.

I'm younger than Chavez. I have an energy that he doesn't have. He's in a comfort zone. And you know the best thing? He thinks he can't lose. I hope he keeps believing that.

Chavez is in fact one of the best campaigners Latin America has ever seen: he came from behind to sweep the 1998 election and has won most of a dozen national votes since then, helped by his own charisma and tramp-the-streets style.

Yet he is nearly two decades older than Capriles and with doctors pleading him to go easy after traumatic cancer surgery last year, Chavez is unlikely to match past energy levels and may rely on more virtual campaigning this year via TV.

WORK, NOT POLITICS

Though himself a center-left politician, Capriles - a lawyer by training with 13 years as a legislator, mayor and now governor of Miranda state - says Chavez's socialism has largely been a disaster for Venezuela despite some gains for the poor.

They call themselves socialists but they are far from modern socialism. This is a completely failed statist model.

From a wealthy family with a cinema chain and other business interests, Capriles professes himself a follower of Brazil's model of free-market economics with a strong social commitment.

He wants to build on and improve what he sees as the best of Chavez's 13 years - free healthcare in slums, for example - while gradually rolling back some of the most radical economic policies like currency controls and nationalizations.

Polls show Capriles' own record in office, energetic style, avoidance of confrontational rhetoric, and emphasis on education, employment and security give him the best chance of beating Chavez among the five opposition primary candidates.

A keen sportsman who frequently rides a motorbike to work and spends more time in shanty towns than his office, Capriles has cultivated an on-the-street image that galvanizes his followers and, analysts say, could sway some wavering Chavez supporters.

I prefer to do, rather than talk, he insists, marking a difference with Chavez's daily speeches, one of which this month hit a probable world record of 9 1/2 hours. Less politics and more work is what Venezuela needs.

Though way ahead, Capriles is not a complete shoo-in for the candidacy of an opposition that finally appears to have finally learned from years of in-fighting that have helped Chavez cement his dominance of the South American OPEC member nation.

Capriles' closest rival is another young state governor Pablo Perez, 42. He has the backing of some of Venezuela's biggest parties, experienced in getting their voters out.

Another aspirant for the opposition ticket, the only female candidate Maria Corina Machado, shot to national prominence in recent days after some bitter sparring with Chavez during this month's speech to parliament.

Suggesting his much-vaunted nationalizations were tantamount to theft, Machado drew some withering put-downs from Chavez and his allies have turned on her since then.

Perez is the closest to Capriles in polls, but even then he is a good 10-20 percentage points behind. So most politicians and investors are already factoring in a Chavez versus Capriles race.

The actual primaries are now a mere formality, wrote Boris Segura of Nomura bank in a note for investors on the Venezuelan opposition race titled Done deal.

Fisherman Samuel Nunez agrees with the Wall Street view.

Waiting for Capriles to alight from his campaign bus by an azure ocean on the sea-front of Cumana, he says his family - eight votes including his wife and children - are backing the governor.

Nunez, 72, acknowledges Capriles is untested nationally but says his local record is great and the nation needs change. You know what they say: to know if the water is salty, you have to taste it. You can't tell by looking. So let's give him a chance.

CHAVEZ CAMPAIGNING TOO

With the opposition primary race dominating private media in Venezuela, Capriles and his fellow Democratic Unity aspirants are not the only ones on the campaign trail.

Barely a day goes by without Chavez popping up on the airwaves. It might be a phone-in to state TV, a televised ceremony or cabinet meeting, or lengthy address to the nation - his presence remains ubiquitous.

As well as splashing ever more money on social programs in a mammoth pre-election spend, Chavez's tactic is to ridicule his opponents and tarnish them all with the same brush as proxies for Venezuela's discredited old oligarchy.

They're all the candidate of the rancid, radical bourgeoisie. They are the candidate of the Yankee empire, he railed during his weekly Alo Presidente (Hello President) TV program at the weekend. They all represent, as (philosopher) Nietzsche said ... nihilism. They are nothing, we are the fatherland.

Rhetoric apart, Chavez does seem to have the edge for the October 7 vote, albeit a narrow one, given loyalty to him among the poor, the acceleration of spending on new and old social projects, an economic upturn and fears of change.

Yet roughly a third of voters are undecided, polls show, so if the opposition can run a dynamic campaign, and woo undecided voters and disaffected Chavistas, the scenario could change.

Chavez's health is also a big variable.

While he insists he is fully recovered from cancer treatment last year, and looks vigorous again albeit still swollen-faced, rumors persist that Chavez is still seriously ill.

The constant whispers among foreign intelligence services and occasional stories in right-leaning media that Chavez still has a life-threatening cancer draw nothing but mockery from him.

Capriles prefers not to dwell much on the issue.

He looks fine to me, he commented after a tasty fresh fish-soup with locals in Cumana. I wish him long life so Chavez can see the changes coming to Venezuela!

(Additional reporting by Diego Ore; Editing by Kieran Murray)