Already struggling to avoid a debt default that could seal Greece’s fate as a financial pariah, this Mediterranean nation is also scrambling to contain another threat — a breakdown in the rule of law.

Thousands have joined an “I Won’t Pay” movement, refusing to cover highway tolls, bus fares, even fees at public hospitals. To block a landfill project, an entire town south of Athens has risen up against the government, burning earth-moving equipment and destroying part of a main access road.

The protests are an emblem of social discontent spreading across Europe in response to a new age of austerity. At a time when the United States is just beginning to consider deep spending cuts, countries such as Greece are coping with a fallout that has extended well beyond ordinary civil disobedience.

Perhaps most alarming, analysts here say, has been the resurgence of an anarchist movement, one with a long history in Europe. While militants have been disrupting life in Greece for years, authorities say that anger against the government has now given rise to dozens of new “amateur anarchist” groups, whose tactics include planting of gas canisters in mailboxes and destroying bank ATMs.

Some attacks have gone further, heightening concerns about a return to the kind of left-wing violence that plagued parts of Europe during the 1970s and 1980s. After urban guerrillas mailed explosive parcels to European leaders and detonated a powerful bomb last year in front of an Athens courthouse, authorities here have staged a series of raids, arresting dozens and yielding caches of machine guns, grenades and bomb-making materials.

The anarchist movement in Europe has a long, storied past, embracing an anti-establishment universe influenced by a broad range of thinkers from French politician and philosopher Pierre-Joseph Proudhon to Karl Marx to Oscar Wilde. Defined narrowly, the movement includes groups of urban guerillas, radical youths and militant unionists. More broadly, it encompasses everything from punk rock to WikiLeaks.

“Many of these are just a few frustrated high school students with a Web site,” said Mary Bossi, one of Greece’s leading terrorism experts. “But as we continue to see, others have the potential to be dangerous.”

Not ready for austerity

The rolling back of social safety nets in Europe began more than a year ago, as countries from Britain to France to Greece moved to cut social benefits and slash public payrolls, to address mounting public debt. At least in the short term, the cuts have held back economic growth and job creation, exacerbating the social pain.

And Greece is not the only place in which segments of society are pushing back.

Though unions and political movements have always used tough tactics in Europe, observers are particularly noting a surge in lower-grade militancy among a “lost generation” of young Europeans who have come of age in the aftermath of the global economic crisis. For most — like the Italian students who draped the Leaning Tower of Pisa and Rome’s Coliseum in anti-austerity slogans last November — protests have become a cathartic outlet to express genuine discontent. For others, they have become an invitation for more radical acts.

In Britain, for instance, 10 activists formed the UK Uncut group in a North London pub late last year, spawning a national wave of civil disobedience against spending cuts, bankers’ bonuses and tax evasion by the rich. During a March protest, they used Twitter and text messages to organize a “flash mob” that saw hundreds occupy and vandalize London’s famous Fortnum & Mason’s food store. In recent months, other actions have forced at least 100 bank branches across Britain to temporarily close.

Last week, officials in the western city of Bristol said they uncovered a plot by violent demonstrators to throw Molotov cocktails at a supermarket and arrested 30 protesters after a pitched battle with riot police.

“There is a sense of general injustice, that the government bailed out capitalism and the citizens are footing the bill while the capitalist system is running like nothing ever happened,” said Bart Cammaerts, an expert in anarchist movements at the London School of Economics. “And yet, things have happened. There are more taxes, less services, and anger is emerging from that tension.”

‘Edge of bankruptcy’

No country is under more pressure to roll back spending than near-bankrupt Greece, a once booming nation now saddled with 35 percent youth unemployment and facing the prospect of years of depressed growth. Buckling under a culture of tax evasion and rampant overspending, Greece received a $170 billion bailout from the IMF and European Union last year.

Since then, pensions have been cut, the retirement age extended and public sector pay slashed. Even so, Greece is still drowning in a sea of debt, and some analysts believe it may yet have no choice but to default on at least a portion of its bonds held by investors. To stave that off, Greece is reportedly in talks with the EU and IMF for a second massive bailout — one that would almost surely come with a requirement to slash domestic spending even further.

“In some countries, the rolling back is happening more gradually, but in Greece, with the nation at the edge of bankruptcy, it is happening like sudden death,” said Yannis Stournaras, an economist who negotiated Greece’s entry into the euro back in the late 1990s.

To be sure, polls show that a majority of Greeks — tired of waste, corruption and public largess — largely support the reforms. But without doubt, experts say, extremism is on the rise and could disrupt attempts to get the nation back on track.

As in many countries in Europe, fascist and far-right parties are strengthening, engaging in an increasing number of attacks against immigrants.

More often, though, angry young Greeks, such as 19-year-old law student Nikolas Ganiaris, are signing up with left-wing youth groups. After the government raised transit fares during the austerity drive, Ganiaris’s group began jumping aboard public buses, blocking customers from punching their tickets as part of the “I Won’t Pay” campaign. Organizers of the movement claim 10,000 supporters are now just saying no to transit fares and highway tolls in protest.

“They are taking everything away from us,” Ganiaris said. “What will happen when I finish law school? Will I only find a job making copies in a shop? Will I then need to work until I’m 70 before I retire? Will I only get a few hundred euros as pension? What future have I got now?”

The new avengers

A radical minority is energizing the anarchist movement, a loose network of anti-establishment groups that sprung up in force in the 1970s in opposition to Greece’s former military junta. Over the next two decades, anarchists would assassinate Richard Welch, a CIA station chief in Athens, as well as Greek politicians and a British military attache.

Greek authorities seemed to cut the head off the movement after the leaders of November 17th, the largest group, were arrested in the early 2000s before Greece hosted the 2004 Olympics. But it has been gaining new life. The December 2008 killing of a 15-year anarchist by a police officer in the Exarchia neighborhood of Athens sparked days of riots and became the impetus for a series of fresh attacks.

Since then, experts say, the economic crisis has helped the movement thrive, with anarchists positioning themselves as society’s new avengers. Long a den of anarchists, the graffiti-blanketed Exarchia neighborhood is alive anew with dissent. Nihilist youths are patrolling the local park, preventing police from entering and blocking authorities from building a parking lot on the site. On one evening at a local cafe, an anarchist group was broadcasting anti-government messages via a clandestine radio station using a laptop and a few young recruits.

In the most recent attacks, only one person has been injured, a courier who handled a letter bomb, but over the past two years, anarchist attacks have claimed four lives in Greece, including a journalist and a minister’s top aide. Left-wing radicals also appear responsible for the deaths of three civilians — including a pregnant woman — after a bank was firebombed during an anti-government protest last year.

Still, there is a line to be drawn between the far larger group of young anarchists hurling Molotov cocktails at street demonstrations and the smaller, more dangerous cells of urban guerrillas. But experts are increasingly concerned about growing militancy on the streets and the emergence of dozens of new anarchist groups on the Internet.

For some Greeks, like Nikos Galanos, a 20-year-old chain-smoking in an Exarchia cafe, the anarchist movement has become an outlet for anger. Last year, during a wave of government cutbacks, Galanos’s mother lost her job as a guard at the ancient Acropolis perched above Athens. His father, also a government worker, saw his salary slashed by 15 percent and must now labor more years before meeting the retirement age, boosted last year to an average age of 63.

Galanos, an electrician, has few job prospects outside the massive black market economy in Greece. But with the nation’s economy still contracting, even the off-the-books work he counted on to put himself through technical school has dried up.

Over the past two years, he has become more involved in the Anti-Establishment Movement, which, while it is among Greece’s less militant anarchist groups, still wields firebombs during protests. The movement’s rallies, which two years ago drew 2,000 to 3,000 young loyalists, now command small armies of 7,000 or more.

“I don’t support violence for violence’s sake, but violence is a response to the violence the government is committing against society,” Galanos said. He later added, “It is now hard for any of us to see a future here. I feel it’s my duty to fight against the system.”

Special correspondents Elinda Labropoulou in Athens and Karla Adam in London contributed to this report.