ROME — Silvio Berlusconi won a crushing victory in the Italian general election yesterday to become prime minister for the third time.

The coalition led by the 71-year-old media magnate defeated the Democratic Party, headed by Walter Veltroni, 52, by a considerable margin and has a large enough majority to rule Italy for a full five-year term.

Mr. Veltroni, who was a popular mayor of Rome before entering national politics, conceded defeat five hours after the polls closed, saying that the result was clear.

He also offered his help to Mr. Berlusconi in “carrying out reforms” but admitted that Italy’s left wing was destined for a long spell in opposition.

Mr. Berlusconi said that “this is a great result for the country.”

“We were interrupted in our work, and we will restart it now. We have the necessary numbers in parliament to pass the laws, which previously were stuck in parliament. I am convinced that we can proceed quickly to modernize the country and to bring us to the level of other European countries and as you know we are very, very determined.”

Projections showed that Mr. Berlusconi’s coalition won 163 seats in the Senate, compared to 141 seats for Mr. Veltroni. In Italy’s lower house, the Chamber of Deputies, the count was 332 seats to 215.

The Senate was a key battleground for Mr. Berlusconi. Both houses of Italy’s parliament have an equal amount of executive power.

However, seats in the Senate are distributed on a regional basis. Any party that wins a majority in a region automatically gets 55% of its seats. Since each party holds a roughly similar number of regions, many commentators doubted whether Mr. Berlusconi would be able to win a solid majority. However, Mr. Veltroni gave warning that Mr. Berlusconi’s government could be held to ransom by the Northern League, the secessionist party headed by his coalition partner, Umberto Bossi.

“The League is strong. We are a great force!” Mr Bossi said after winning between 7% and 8% of the vote.

Mr. Bossi, who is one of Italy’s most controversial and unpredictable politicians, called on Mr. Berlusconi to give him a large share of cabinet posts and to carry out the devolution of Italy “immediately.” His party is bent on splitting the industrial north from the poor regions of the south. Mr. Bossi has wrecked Mr. Berlusconi’s government before, when he broke off their alliance in 1994.

Although Mr. Veltroni lost the election, he was praised for bringing about a revolution in Italian politics. In the past, the Italian parliament was filled with dozens of squabbling parties.

Romano Prodi’s government was made up of 11 separate parties, ranging from Catholics to communists. Unsurprisingly, it was unable to find a consensus on any political issue and collapsed under the weight of its contradictions.