* Powerful trio meet Raul Castro, check on Chavez
* Venezuelan leader still unseen since Dec. 11 operation
* Opposition demand "truth" on president's condition
* Solidarity rallies continue across Venezuela
CARACAS, Jan 13 (Reuters) - Venezuela's three most powerful government figures after President Hugo Chavez gathered in Havana on Sunday to check on their ailing leader's condition and meet with Cuban allies.
Vice-President Nicolas Maduro, Congress head Diosdado Cabello, and Oil Minister Rafael Ramirez have been shuttling to and from Cuba since the 58-year-old socialist president's fourth and most serious cancer operation a month ago.
Chavez, who missed his own inauguration for a new, six-year term last week, has not been seen or heard from in public since the surgery. Many Venezuelans are assuming his momentous 14-year rule of the South American OPEC nation could be nearing an end.
Though acknowledging the gravity of the situation and a severe lung infection Chavez is suffering, officials are trying to stay upbeat on the president's hopes for recovery. His brother on Saturday denied that Chavez was in a coma.
"We are all Chavez!" and "Chavez will return!" were among slogans sang and chanted at numerous solidarity rallies, meetings and concerts across Venezuela over the weekend drawing thousands of passionate and anxious supporters.
Venezuelan state TV on Sunday split its screen into four to show events going on around the nation. "Commander, take your time returning to us," Trujillo state Governor Henry Rangel said at one.
Information Minister Ernesto Villegas said Maduro, who Chavez recently designated as his successor, informed Venezuela's leader of the outpouring at home. He gave no more details of their encounter or the president's condition.
State media said Maduro, Cabello, Ramirez - who also heads the powerful state oil company PDVSA - and Attorney General Cilia Flores all met Cuban President Raul Castro over the weekend. But there were no details of the talks.
'TELL THE TRUTH'
The joint presence of top Venezuelan officials in Havana inevitably deepens rumors Chavez is at death's door - and draws opposition criticism that Raul and Fidel Castro are giving instructions behind the scenes.
But officials have been lashing "necrophilic" opponents for such speculation, and Chavez's brother said on Saturday that, on the contrary, he was improving daily.
One opposition leader, Julio Borges, said on Sunday the secrecy around Chavez's exact condition was unacceptable.
"No one is asking for details of the operation or the president's treatment, but that simply they tell the truth about his health prognosis," said Borges, a right-wing legislator who wants Chavez formally declared absent from office.
That would trigger the naming of a caretaker president, and an election within a month, but Venezuela's Supreme Court has ratified that Chavez remains president with Maduro in charge as No. 2 until his health situation is clarified.
"It's been a year-and-a-half of contradictions and announcements of his complete curing followed by relapses," Borges added, saying problems like inflation, housing shortages and power-cuts were being neglected during a political impasse.
Since the disease was discovered in mid-2011, Chavez has in fact wrongly declared himself cured twice, in an extraordinary and unsettling saga for Venezuela's 29 million people.
The stakes are high for the wider region too. Cuba and a handful of other leftist-ruled nations have for years been depending on Chavez's aid to bolster fragile economies.
Should Chavez die or be incapacitated, the most likely next step would be an election pitting Maduro, 50, against Henrique Capriles, 40, the main opposition leader who lost to Chavez in an October presidential election.
In a statement on Sunday, Capriles railed against the "national paralysis" but said the opposition would not be drawn into confrontation or street protests. That tactic failed spectacularly for them a decade ago when Chavez was briefly toppled but came back stronger than before.
"Just as the president has the right to attend his ill health, so Venezuelans do not deserve urgent problems to be put on hold," Capriles said. "We are not going to play the game of calling people onto the street to create a confrontation that will benefit the violent and radical ones."