By Andrew Cawthorne

CARACAS (Reuters) - A dozen activists alight surreptitiously from cars, walk determinedly toward Venezuela's heavily-guarded Food Ministry, and dump two bags of garbage at its front entrance.

Soldiers quickly form a cordon and a young opposition lawmaker pounds their riot shields with his fists as government supporters appear from nowhere, throwing punches at the protesters.

The activists, who use garbage to symbolize how people are scavenging for food because of Venezuela's economic crisis, chant "The People Are Hungry!" and "Democracy!" After a few minutes, they are chased back to their cars by a fast-growing crowd of supporters of socialist President Nicolas Maduro.

The mid-morning fracas in a working-class district of Caracas is the latest of near-weekly "surprise" protests by the opposition this year intended to embarrass Maduro, galvanize street action and highlight Venezuela's litany of problems.

"Three million Venezuelans are eating out of rubbish today," said the 28-year-old legislator Carlos Paparoni, nursing a few bruises after the Food Ministry protest.

"No one can shut us up. We will fight wherever we have to."

While the small, flash protests briefly paralyze streets, turn heads and provide colorful photo ops for journalists tipped off in advance, they are little more than a minor irritant to Maduro.

In fact, they have only been on the rise this year because of the failure of traditional mass marches in 2016.

A year of marches, which peaked with a million-person rally in Caracas, did not stop authorities blocking a referendum on Maduro's rule that could have changed the balance of power in the South American member of OPEC with 30 million people.

Instead, they led to a short-lived Vatican-championed dialogue that helped shore up the unpopular president and divided the opposition Democratic Unity coalition, leaving rank-and-file activists demoralized.

With Maduro's term due to finish in early 2019, authorities are now delaying local elections and making opposition parties jump through bureaucratic hoops to remain legally registered.

"We'll have to stop conventional rallies and use the surprise factor to make the government see it must respect the constitution," said opposition leader Henrique Capriles, whose First Justice party is a main promoter of the flash protests.

'NO TO DICTATORSHIP!'

After traditional-style marches around the country on Jan. 23 were again blocked by security forces, Capriles debuted the new strategy the next day with a surprise protest that briefly immobilized vehicles on a highway.

Demonstrators held banners demanding "Elections Now!"

Since then, activists coordinating clandestinely and rotating responsibilities, have popped up regularly to stop traffic, chant slogans and demand meetings with officials. One day, they held three simultaneous protests.

Numbers, however, are small, seldom more than a dozen or two. Security forces normally move them on quickly, and pro-Maduro supporters hang around government buildings precisely to display their political zeal in such moments.

"These fascist coup-mongers are seeking violence. They should go to jail!" shouted Jorge Montoya, 48, wearing a "Chavez Lives!" T-shirt in honor of late leader Hugo Chavez outside the Food Ministry where he helped chase off the protesters.

Officials did not respond to requests for interviews on the flash protests. Maduro and other senior government officials routinely denounce opposition activists as coup-plotters, intent on bringing down socialism in Venezuela.

Another opposition party, Popular Will, which has long promoted civil disobedience tactics, is also a main instigator of street activism.

Its members last month painted a mosaic of their jailed leader Leopoldo Lopez on a highway, decked lamp posts with black "No To Dictatorship!" signs overnight, and on Valentine's Day handed flowers to security personnel.

"They are actions that have to be creative, have high impact for communication, dent the government's sense of invincibility, transmit a message ... and reduce fear," said Emilio Grateron, Popular Will's national head of activism.

The party's more than 150,000 activists take inspiration from successful models of non-violent protest abroad such as those in the 1980s by then-trade union leader Lech Walesa against communism in Poland and opposition in Chile to the military dictatorship of Augusto Pinochet.

Such heady comparisons, though, seem far-fetched in Venezuela right now where not just government officials but even some cynical opposition supporters scoff at the flash protests as ineffectual stunts.

"No one sees these surprise protests," said Julio Pereira, 25, a student and long-time supporter of opposition marches. "The government laughs at them."

Even though the opposition coalition proved it had majority support by winning legislative elections at the end of 2015, and despite the disastrous state of Venezuela's economy, the prospect of political change has dimmed this year.

"Not so long ago, I was ready to march to Miraflores (presidential palace)," said Pereira, now about to join friends who have found work in Argentina. "Now I'm instead heading to the airport to get out. The government is a disaster, the opposition is a disaster, my country is a disaster. I'm gone."

(Reporting by Andrew Cawthorne; editing by Christian Plumb and Grant McCool)