ROME – A defiant Silvio Berlusconi refused to concede defeat in Italy’s general election yesterday even though his rival Romano Prodi was declared the winner in both houses of parliament.

The opposition leader claimed victory by the slimmest of margins and the interior ministry said Mr. Prodi’s center-Left Olive Tree coalition had won the lower house by just 25,000 votes. It also declared Mr. Prodi victorious in the senate race, thanks to votes in overseas constituencies created by Mr. Berlusconi’s government.

In keeping with the histrionics of his campaigning, the billionaire prime minister refused to go quietly. He called for the help of the court of appeal and the Supreme Court to decide the election.

He said Mr. Prodi would “pay the consequences” for declaring victory and declared the country was so split that he did “not think the country can go forward in this type of civil war.”

Mr. Prodi, a technocrat who briefly served as prime minister in the mid-1990s, dismissed a suggestion by his rival for a “grand coalition” of Right and Left to govern Italy.

He said Mr. Berlusconi had lost his grip on reality. “We went before voters with a precise coalition. We will govern with the coalition majority,” he said.

Mr. Berlusconi noted that in the last election, 36,000 votes had been found by the courts after the count had finished. The challenges to the result will now pass through the legal system, and a clear result may not emerge before April 28, the date when President Carlo Ciampi will call for a new government.

Mr. Berlusconi said there had been “very many irregularities” with the count, especially with the votes received from foreign voters.

One member of Mr. Berlusconi’s coalition said several thousand votes had gone missing in Switzerland. “We should not believe this spectacle that we have seen from the left,” said Mr. Berlusconi. “These votes may not be votes which we can accept as valid.”

For the first time, foreign-based Italians were able to choose six members of the Senate and 12 members of the House of Deputies.

The north of Italy, which contains the country’s financial and industrial might, voted decisively for Mr. Berlusconi. However in the Mezzogiorno, the states in the South where unemployment and poverty are rife, there was a swing to the center-left.

Mr. Berlusconi launched his new strategy after spending the day in talks with party leaders at his headquarters in Rome.

The two houses in Italy’s parliament are equally powerful, and if Mr. Berlusconi manages to win one of them he will be able to hamstring Mr. Prodi’s government and force a repeat of the election.

Mr. Prodi, former head of the European Commission, added that he would put Europe at the heart of his policies. He said he was unconcerned at Mr. Berlusconi’s determination for a recount, although his winning margin had been slight.

Even if Mr. Prodi is found to be the victor by the Italian courts, he may find it difficult to carry out any reforms.

James Walston, the head of international relations at the American University in Rome, said: “He will have to step very carefully and play the Parliamentary game very well. Mr. Berlusconi may obstruct and filibuster him in the Senate, but Mr. Prodi’s real problem is his own side. He will not be able to pass anything controversial because one or two senators might say they will not turn up.”