CARACAS, Venezuela (AP) -- Venezuelan opposition leader Henrique Capriles is set to announce he will run in elections to replace Hugo Chavez, setting up a make-or-break encounter against the dead president's hand-picked successor, a close adviser to the candidate says.

"He will accept" the nomination, the adviser told The Associated Press. He spoke Sunday on condition of anonymity because he was not authorized to discuss the decision publicly ahead of a formal announcement scheduled for later in the day.

Other opposition sources refused to comment, but a political consultant at ORC Consultores, which advises Capriles, also said he would run.

"He will put himself forward," said Oswaldo Ramirez. "History is giving Capriles Radonski an important role."

Venezuela's election commission has set April 14 as the date of the vote, with formal campaigning to start just 12 days earlier. Ramirez said the 40-year-old opposition leader would demand that officials extend the campaign period by moving up the start date by more than a week, and that acting president Nicolas Maduro not be allowed to abuse state resources to boost his chances during the campaign.

Maduro has already announced his intention to run as the candidate of Chavez's socialist party. On Sunday he picked up the support of Venezuela's small communist party as well.

In a speech accepting the party's nomination, Maduro insisted he was running for president out of loyalty to Chavez, not vanity or personal ambition, and called on the people to support him

"I am not Chavez," Maduro said, wearing a simple red shirt. "In terms of intelligence, charisma, historical force, or capacity to lead ... But I am a Chavista and I live and die for him."

Capriles faced a stark choice in deciding whether to compete in the vote, which most analysts say he is sure to lose amid a frenzy of sympathy and mourning for the dead president.

Some say a second defeat for Capriles just six months after he lost last year's presidential vote to Chavez could derail his political career. If he waits, a Chavista government led by Nicolas Maduro, the acting president, might prove inept and give him a better shot down the road. But staying on the sidelines also would have put his leadership of the opposition.

"If he says he doesn't want to run I could totally understand that," said David Smilde, an analyst with the U.S.-based think tank the Washington Office on Latin America. "He is likely going to lose and if he loses this election he's probably going to be done."

On a personal Twitter page that bore all the rah-rah adornments of a campaign site, Capriles wrote Saturday afternoon: "I am analyzing the declaration of the (electoral commission setting the date) and in the next hours I will talk to the country about my decision." A spokesman said Capriles would make an announcement in the early evening.

Analysts predict the next five weeks will increase the nasty, heated rhetoric that began even before Chavez's death Tuesday after a nearly two-year fight with cancer.

Maduro, who was named Chavez's vice president after the October election, was sworn in as this oil-rich country's acting leader Friday night. He is expected to file election papers on Monday

Opposition critics have called Maduro's ascension unconstitutional, noting the charter designates the National Assembly president as acting leader if a president-elect cannot be sworn in.

On the streets of Caracas on Sunday, opinion was as divided as always in a country that became dramatically more polarized during Chavez's 14-year rule.

"It's not fair," said Jose Mendez, a 54-year-old businessman of the choice the opposition leader faces. "(Maduro) has an advantage, because of everything they have done since Chavez's death, all the sentiment they've created ... But the guy has nothing. He can't hold a candle to Chavez."

But Ramon Romero said the opposition was just making excuses, and had no chance of victory in any case.

"Now their odds are even worse," said the 64-year-old waiter and staunch Chavez supporter. "They don't care about anyone, and we (the voters) have been lifted out of darkness."

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Associated Press writers Paul Haven, E. Eduardo Castillo and Jack Chang contributed to this report.