ROME — Italian voters delivered a rousing anti-austerity message and a strong rebuke to the existing political order in national elections on Monday that threatened to plunge the country into political paralysis after early results failed to produce a clear winner. Political experts said the situation would most likely lead to a shaky coalition government and once again expose Italy and the euro zone to turmoil if financial markets question the new government’s commitment to spending reductions that have kept the budget deficit within a tolerable 3 percent of gross domestic product.

In an election marked by voter anger and low turnout, the center-left Democratic Party appeared to be leading in the Lower House with a third of the votes counted and in the Senate with two-thirds of the votes counted by 8 p.m. local time. But the results were not a clear victory, because the center-right People of Liberty Party of former Prime Minister Silvio Berlusconi was leading in several populous regions that carry more Senate seats, raising the prospect of political gridlock.

Even without a final result, the election was a victory for the Five Star Movement of the former comedian Beppe Grillo, which in its first-ever national elections appeared, at this stage of the count, to win 25 percent of the vote in the Lower House. Italians from both right and left — and the wealthier north and poorer south — were drawn to Mr. Grillo’s opposition of austerity measures and cries to oust the existing political order.

And it was a stinging defeat for the caretaker prime minister, Mario Monti, a newly minted politician whose lackluster civic movement appeared to win around 10 percent in both houses. “Grillo had a devastating success; the rest of the situation is very unclear,” said Stefano Folli, a political columnist for the business daily Il Sole 24 Ore.

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