* Opposition angry at Maduro's aggressive rhetoric
* Chavez still battling infection after cancer operation
* Venezuelans heading into uncertain, volatile 2013
CARACAS, Dec 21 (Reuters) - Venezuela's opposition mocked President Hugo Chavez's chosen successor Nicolas Maduro on Friday as a "poor copy" of his boss who should be promoting national unity rather than insulting opponents during a delicate time for the South American nation.
In power since 1999, Chavez named vice president and foreign minister Maduro as his preferred replacement should he be incapacitated by the cancer he is battling in Cuba.
Since the Dec. 11 operation, Maduro, 50, a former bus driver and union leader who shares Chavez's socialist politics, has been fronting day-to-day government in Venezuela while the president has been neither seen nor heard from in public.
Though lacking Chavez's booming charisma, Maduro has borrowed elements of his style - speaking regularly and lengthily on live TV, inaugurating public works, rallying supporters and attacking "bourgeois" opponents at every turn.
He even used one of Chavez's old catch phrases to gloat that Sunday's regional vote, where Chavez allies won 20 of 23 governorships, smashed the opposition into "cosmic dust."
The opposition Democratic Unity coalition reacted angrily.
"Vice President Nicolas Maduro has begun his temporary rule badly," it said in a withering statement, accusing him of ignoring Venezuela's pressing social, economic and political problems while falling back on antagonistic speeches.
"Mr. Maduro, the country expects better from you than a bad imitation of your boss. ... In his rhetoric, Maduro hides the leadership crisis in government given President Chavez's absence. He hides his weakness with shouts and threats."
"Don't waste the opportunity to create a wide national consensus," the statement said.
After an extraordinary year - in which Chavez proclaimed himself cured from the cancer that has dogged him since mid-2011, won a presidential election, then disappeared for new surgery - Venezuelans are heading into an uncertain 2013.
Government officials say Chavez, 58, is lucid and recovering in a hospital, but have acknowledged he is still suffering a respiratory infection after his operation and needs total rest.
Speculation is rife that his condition is life-threatening, and there is uncertainty over whether Chavez will be able to return to start his new term on Jan. 10.
The stakes are huge in Venezuela's political drama.
Beyond its borders, Venezuela helps sustain an alliance of left-wing Latin American governments from Cuba to Bolivia via oil subsidies and other economic aid.
Should Chavez be forced to vacate power, a new election would be held within 30 days, with the probable scenario a straight competition between Maduro and opposition leader Henrique Capriles, who lost to Chavez in the October vote.
There are rumors of in-fighting within "Chavismo" - the wide movement of military men and hard-left ideologues that has ruled for the last 14 years. Yet in public, the senior figures have repeatedly vowed unity and loyalty to Chavez.
Apart from Maduro, the two most powerful men are Congress head Diosdado Cabello and Energy Minister Rafael Ramirez.
"You know, there is a campaign from abroad and by the national right wing to try and divide us," Maduro said in one of a string of speeches on Friday at ceremonies to celebrate the pro-Chavez governors' election wins.
"Every day, they say we're fighting, that Diosdado is Joseph Stalin and I am Leon Trotsky. Ridiculous, ridiculous and more ridiculous! ... We've never been more united."
Cabello, a former military comrade of Chavez viewed by Venezuelans as the hard man in government with possible presidential ambitions of his own, stirred controversy this week by suggesting that the Jan. 10 inauguration date could be delayed to accommodate Chavez's recovery.
Confusion over that and any tensions within the ruling Socialist Party threaten to create a difficult transition to any post-Chavez government in the OPEC nation with the world's largest crude oil reserves.
Former soldier Chavez has vastly expanded presidential powers and built a near-cult following among millions of poor Venezuelans, who love his feisty language and pouring of funds into welfare projects in the nation's slums.
Smarting from defeats in the presidential and state polls in quick succession, the opposition coalition is trying to keep Venezuelans' attention on a raft of unresolved problems, from a soaring black market in currency to rampant crime.
"The economy is in dust. Citizens' security is in dust. Public services are in dust. The only thing that isn't is corruption in government," the coalition statement said.