Mr. Berlusconi will make a fuller statement Tuesday. But he promised immediate action on many of the problems vexing Italians, like the trash crisis in the south that has tarnished the nation’s image and the sale of the near-bankrupt national airline, Alitalia.

The election  called just two years after Mr. Berlusconi lost to Mr. Prodi  was considered one of the least exciting in memory, with many Italians doubting that either candidate could accomplish any meaningful change.

But in some basic ways, the election signaled a decisive shift in a nation whose politics have been unstable because of the narrow interests of its many small parties. Mr. Veltroni, heading the new Democratic Party, the result of a merger of the two largest center-left parties, had refused to run with far-left parties, as Mr. Prodi had done.

Image Silvio Berlusconi in Milan last month. Credit... Luca Bruno/Associated Press

As a result, the ANSA news agency reported that the number of parties in the lower house of Parliament, the Chamber of Deputies, would drop to just 6 from 26. For the first time since World War II, there will be no one in Parliament representing the Communist Party, which has long played an important part in leftist politics here. Mr. Veltroni, in fact, started his political career as a Communist.

Experts on the left and the right said  and in some cases lamented  that the election had shown a shift toward a more American- or British-style system of two dominant middle-ground parties.

“It’s a Waterloo,” said Tuesday’s headline in the moderate left daily Il Riformista.

Its editor, Antonio Polito, a departing senator from the now-defunct Margherita Party, said, “The left is disappearing for the first time in history.” Referring to Mr. Veltroni’s party, he added, “The only party that managed to save itself after two disastrous Prodi years is a party that is modeling itself after the Democratic or Labor Parties” in the United States and Britain, respectively.