Five Star Movement deputies talk at the Chambers of Deputies in Rome on March 15. The rise of the Five Star Movement, led by a former comedian, is evolving into a social experiment of what happens when voters decide to radically alter the status quo. (Remo Cassili/Reuters)

Mr. Smith went to Washington. Now, Carlo Sibilia has come to Rome.

The 27-year-old elevator salesman without a single day of experience in political office arrived in the Italian capital this month with 162 other freshman legislators from the Five Star Movement — a Web-based force whose success in recent elections has the newcomers suddenly bidding arrivederci to politics as usual in Italy.

For 60 million Italians and political junkies of every stripe, the triumphs of a movement encompassing disenfranchised voters from both the left and the right — think the tea party, if it included everyone from Michael Moore to Rush Limbaugh — are a thrilling example of the power of grass roots. In a country known for bespoke-suited lawmakers with CEO salaries and a penchant for Machiavellian backroom deals, the army of newcomers includes geologists, steel workers and homemakers seeking to end the days of La Dolce Vita for Europe’s most privileged political class.

The rise of the Five Star Movement, led by a former TV comedian, is the latest manifestation of a growing backlash in Europe to crippling austerity and entrenched cronyism in the halls of power. It is nothing less than a social experiment underscoring what happens when voters decide to radically alter the status quo. But while Italy’s political earthquake carries the promise of desperately needed change, it also runs the risk of destabilizing one of the world’s largest economies and reigniting the worst of Europe’s debt crisis.

On shoestring budgets and an anti-establishment platform starting with pledges to slash lawmakers’ salaries of more than $250,000 a year, the Five Star Movement’s candidates won so many votes in elections last month that they have become Italy’s political kingmakers.

Many had expected these political neophytes to drop their down-home shtick once elected, cutting a deal that would give them a seat at the table of government and trade their polenta for steak. But like James Stewart’s character in the 1939 political drama about an average guy who heads to Capitol Hill, the movement’s members have proved more difficult to manipulate than many had thought.

Instead, their resistance to a deal with traditional parties has left Italy without a government for almost a month and raises the prospect of new elections if the impasse cannot be resolved.

Even if a government is formed in the coming days — as officials from the center-left Democratic Party are trying to do — without the support of the newcomers, any new administration could be so weak that it may fall within months.

If that comes to pass, pollsters say, the Five Star Movement’s lawmakers have a real shot at coming out on top. What would happen then is anybody’s guess.

The movement is seeking to slash government waste and do away with public funding for political parties and the media. But it is also actively calling for a referendum on Italy’s membership in the euro zone and proposing a pro-environment agenda that includes new public parking lots for bicycles in neighborhoods across the country.

Its members are additionally floating a range of radical ideas, including a suspension of payments on the national debt and free Internet access for all Italian citizens. Concern in the financial world is running high, and the ratings agency Fitch has downgraded Italian debt.

Yet freshman legislators such as Sibilia, who comes from a small town in the south and lives out of a suitcase in a $30-a-night flophouse in Rome, are promising at least one thing: not to sell out.

“Walking into the chamber [of legislators] for the first time felt like I was on another planet, as different as Pandora in the movie ‘Avatar,’ ” Sibilia said. He signed up online to run for the Five Star Movement and spent about $130 on his campaign. “But now all of that is fading, and we realize that we’re here to fulfill our promise to voters. We are going to keep our integrity. We’re finally going to change how Italy works.”

Direct challenge

Europe’s debt crisis and waves of austerity have fueled surging grass-roots movements that are altering the political landscape of the continent. Some, like the neo-Nazi Golden Dawn in Greece, are seen as dangerous and destabilizing.

Others, like Spain’s Indignados — who organize via social media and inspired the Occupy movement in the United States — have become outlets for a lost generation of unemployed youths who believe traditional politicians have failed them.

Yet few have seen such a direct challenge to the establishment as here in Italy. Fury at lavish lawmaker lifestyles — including some photographed last year in togas and pig masks and cavorting with women — helped the Five Star Movement exceed virtually all expectations in the elections.

The Five Star Movement, founded in the mid-2000s by Beppe Grillo, a TV comedian turned activist who orchestrated nationwide rallies against the political classes, began as a virtual party of disenchanted voters who met via online forums. Sibilia signed up on the Internet after he returned from university to his home town near Naples to find that a waste-disposal strike had left trash strewn through the streets. Soon, he was organizing small meetings of activists in coffee shops and living rooms.

“The country was not functioning,” he said. “Grillo understood that, and now voters do, too.”

When the dust cleared after the elections, the Five Star Movement had placed second in the lower house and third in the Senate. Even U.S. Ambassador David Thorne appears to have caught Five Star Fever. In a recent speech to high school students, he said, “I know you have challenges with meritocracy, but you can take the situation into your hands and do as the Five Star Movement does in order to bring about reform and change.”

Uncertain path ahead

All of Italy is watching to see whether the Grillini — as the freshman lawmakers are collectively known — will be seduced by traditionally grand political lifestyles, becoming part of the same establishment they have railed against. To be sure, the strategy of their rivals, according to political insiders, is to try to entice the Grillini to defect, one by one.

Last week, a few members of the movement broke ranks to help elect a new head of the Senate. Nevertheless, the movement has rebuffed all attempts by Pier Luigi Bersani, leader of the Democratic Party — which narrowly finished first in the vote — to persuade Five Star members to join a ruling coalition.

The movement’s stubborn refusals have left Bersani unable to find the support to become prime minister, forcing him to try to woo the right-wing Northern League into a bizarre and probably temporary alliance. Another option could see Italy ruled by an appointed technocrat, as happened two years ago when Mario Monti, a university president, was tapped. But such a government is also likely to be short-lived.

If Italy heads to fresh elections, some polls show that the Five Star Movement would be in first place. Yet analysts say the party’s success hinges on whether rage continues to rule above all else among voters. The party won a substantial number of votes from conservatives, for instance, despite a platform that includes long-term unemployment benefits and a reversal of deep cuts made to health care and education.

“Some of the measures in their platform are very radical, even contradictory to what some of their voters believe in,” said Giovanni Orsina, a political analyst at the Rome-based LUISS School of Government. “But right now, their support is being driven by anger against the political classes. And right now, that’s all some voters are thinking about.”

Stefano Pitrelli contributed to this report.