(Updates with Capriles' aide freed, paragraphs 3, 19; Tachira governor, paragraph 10)
By Daniel Wallis and Efrain Otero
CARACAS, Nov 23 (Reuters) - Tens of thousands of opposition supporters marched in Venezuela on Saturday to pressure President Nicolas Maduro's government before Dec. 8 local elections after their leader denounced the pre-dawn arrest of one of his aides.
The vote for control of 335 municipalities will be the first big test of Maduro's political strength after he narrowly defeated his opposition rival, Henrique Capriles, in a presidential election in April.
Capriles told the main rally in the capital his national tours coordinator, Alejandro Silva, was taken at gunpoint from a Caracas hotel room by military intelligence agents. The aide said later on Twitter that he had been released.
"Maduro, don't be a coward! ... You want to put me in prison, come for me! I'm not afraid," Capriles said to cheers from a crowd of 2,000 to 3,000 supporters, many wearing the blue, yellow and red of the Venezuelan flag.
With voters frustrated over surging inflation and product shortages, a major part of the government's strategy has been a theatrical confrontation with business leaders that echoes the style of Maduro's late mentor, Hugo Chavez.
The authorities have ordered businesses to slash prices and people have flooded shops to take advantage of discounted items ranging from car parts to electronics and sports shoes.
Maduro said a new foreign currency exchange mechanism would be unveiled on Monday, but gave no other details.
Many people who marched with the opposition said Maduro's statist economic policies were the problem.
"I'm not looking for home appliances," said Celide Romero, a 79-year-old protester. "I've been looking for milk for the last month and a half, but there isn't any."
In one apparently isolated report of trouble, the governor of western Tachira state, Jose Vielma, said opposition supporters destroyed a government post set up to register small- and medium-seized businesses during their march there.
Competing with the opposition rallies for local media headlines over the weekend is the latest move in what Maduro calls an "economic offensive," with ministers leading inspection teams to check shopping malls nationwide.
The government charges that anyone who marched with the opposition was showing support for corrupt "speculators" who it blames for an annual inflation rate that neared 55 percent last month and a black market rate for dollars that has risen to some nine times the official level of 6.3 bolivars.
"It's class warfare ... we love the homeland and happiness, and others want to concentrate power and riches in a few hands and exploit the people," said Vice President Jorge Arreaza.
The opposition counters that Maduro's "offensive" - which began with the military occupation of an electronics chain - amounts to state-led looting that punishes honest business owners and only makes things worse.
They were angered further last week when the "Chavista"-dominated National Assembly granted Maduro decree powers which he has vowed to use first to cap retailers' profits and reorganize the distribution of foreign currency.
On Friday, the president said he had ordered the arrest of two unnamed opposition officials whom he accused of trying to pay individuals to disguise themselves as government supporters and attack Saturday's opposition rallies, with the goal of blaming his administration for any bloodshed.
"They're looking for a death in order to try to light a fuse. We won't allow it," Maduro said in a televised speech.
There was no official comment on the opposition leader's aide, who was held for several hours, but a senior government minister said a "fascist henchmen" of Capriles was detained.
Late in the day, Silva said on Twitter he had been released: "I'm now free and ready to move forward," he said. (Additional reporting by Girish Gupta and Diego Ore; Editing by Christopher Wilson and Eric Walsh)