ROME, Feb. 21 — Italy's fragile government snapped suddenly on Wednesday under the weight of its own internal divisions as well as a broader skepticism about the European role in the worldwide fight against terrorism.
Prime Minister Romano Prodi, in office just nine months, submitted his resignation on Wednesday evening after his ruling coalition lost a key vote on foreign policy in the Senate.
Two of his own far-left coalition members abstained amid tensions over whether Italy should continue to provide troops to Afghanistan and Mr. Prodi's support of an expansion of an American military base in Vicenza, in northern Italy.
With only a razor-thin majority, the abstentions killed the measure, aimed at gaining Senate support for Italy's foreign policy, and unexpectedly doomed the government.
"I can't in any way give my vote to this government with this foreign policy," said Fernando Rossi, a senator from the Italian Communist Party and one of the dissenters.
The vote came the same day Britain announced a substantial reduction of its troops in southern Iraq and a week after a European Parliamentary committee issued a strong report criticizing secret American flights in Europe of terror suspects.
But the government's collapse also reflected its own inherent weaknesses, possibly signaling that Italy's chronic political instability may be coming out of remission. In a nation that has had some 60 governments since World War II, Mr. Prodi has presided uneasily over a coalition of nine diverse parties, ranging from moderate Catholics to Communists.
"It's very bad," said Roberto D'Alimonte, a professor at the University of Florence and expert in electoral law. "We still have to come to terms with a working political system. We do not have a working political system."
There are many scenarios for what comes next — and one possibility, if not immediately likely, is a return to power of Silvio Berlusconi, whom Mr. Prodi defeated in elections last year.
As ministers met throughout the afternoon to discuss how to go forward, Mr. Berlusconi's supporters rallied outside the seat of government, waving banners and demanding that the government step aside.
"The country has been exposed, by a majority that isn't and by an incompetent government that has rejected parliamentary dialogue — a grave international humiliation," Mr. Berlusconi told reporters.
For Mr. Berlusconi to return, new elections would have to be held, which at the moment seems several steps in the future.
After accepting Mr. Prodi's resignation, President Giorgio Napolitano will begin on Thursday to consult with political parties and will ask one of them to try to form a government.
Many political experts believed that Mr. Prodi would be given a chance to shuffle his cabinet in a way that would satisfy the parties already in the government. Then he would call for a confidence vote in Parliament.
But many experts noted that such a government would remain weak, with the deep splits over Afghanistan and the American base unresolved.
"Something has broken," said Franco Pavoncello, the president of John Cabot University here and a political scientist. "This vote and the reaction of the government has created damage to Prodi's ability to last."
In theory, the prime minister's term lasts five years, but Mr. Berlusconi is the only prime minister to have endured that long. While the government's weakness made it liable to fall at any moment, its collapse on Wednesday came as something of a surprise. For months the government has been bickering internally — and weathering attacks by Mr. Berlusconi and other opposition leaders — over issues ranging from the budget to a proposed law giving rights to unmarried couples.
But foreign policy remained a particular weak spot. Essentially, Mr. Prodi and his ministers have sought to walk a difficult line, echoing much of the skepticism in Europe about President Bush and the war in Iraq while maintaining Italy's traditionally strong ties with America.
The government's far-left members, however, have strongly resisted the presence of nearly 2,000 Italian troops in Afghanistan. And last weekend, tens of thousands of people rallied against the expansion of the American-staffed NATO base in Vicenza, which Mr. Prodi's government reluctantly supported.
The splits grew deeper, and on Tuesday in Spain, Italy's foreign minister, Massismo D'Alema, himself a former prime minister, called for the Senate to endorse Italy's foreign policy. If it did not, he said, the government should "go home," or step down.
In a long and impassioned speech before the vote on Wednesday, Mr. D'Alema defended his government's position on Afghanistan and the Vicenza base, in terms that he hoped would win the left's support.
"We have not supported the neo-conservative politics of the American administration and we have not sent soldiers to Iraq," he told his colleagues. "There is a profound difference between the military operations in Afghanistan, approved by the United Nations, and those in Iraq."
He added that the support of expanding the Vicenza base was essential to good relations with America. "To change course would be a hostile act against the United States," he said.
In the end, the government needed 160 votes, but only got 158 with the two abstentions. Opposition senators roared at the result, shouting immediately: "Resign! Resign!"
Many experts said they believed Mr. D'Alema, one of the most powerful and experienced members of the government, would resign. And as Italy's leaders search for a broader solution in the next few days, there are several alternatives to a mere shuffling of the current cabinet.
The most dramatic, and perhaps least likely, is that Mr. Napolitano could call immediate elections. But he has said he will not do so until the current electoral law, instated by Mr. Berlusconi last year, is changed. Many experts blame the law for virtually guaranteeing a thin majority in the Senate no matter who wins, and thus destabilizing the political system.
Another option is the appointment of a temporary government made up of largely centrist technocrats. The aim would be to steer Italy toward new elections, most likely engineering a change to electoral laws first.
A final possibility involves peeling off the more Centrist Union of Christian Democrats, a party long allied, if uneasily, with Mr. Berlusconi. Even as the government tottered on Wednesday, one party leader, Marco Follini, seemed to raise the possibility. "The moment has arrived to put into the pipeline a different center-left," he told reporters.
But Mr. D'Alimonte noted that the party does not have enough seats to allow Mr. Prodi to cast off the rebellious far-left of his own party. Simply adding on Mr. Follini's party to give Mr. Prodi a larger majority in Parliament also remained a possibility, although Mr. D'Alimonte noted that it also seemed a recipe for even deeper disputes, since the party shares little politically with the Communists who brought down the government.
Peter Kiefer contributed reporting. -- Yoshie <http://montages.blogspot.com/> <http://mrzine.org> <http://monthlyreview.org/>