Mr. D'Alema, the first former Communist to become Italian prime minister, was in office for 18 months. He first offered his resignation Monday after his center-left coalition suffered serious losses in regional elections.

   Mr. Ciampi rejected it then but had no choice but to accept it this time.  Mr. Ciampi said he would begin two days of consultations Thursday with Italian political leaders to find a new center-left prime minister. If that fails, calling a snap general election a year early might be his only option. Political sources said Wednesday that the center-left bloc was considering  proposing Treasury Minister Giuliano Amato as a candidate to take over as prime minister until the next general election. The sources said central bank governor, Antonio Fazio, could then become the bloc's candidate for prime minister in the next election, due to be called in April 2001. ''We are thinking about the possibility of a government to last until the end of the legislature led by Amato, in order to build a strong leadership to go into the 2001 elections, which could be that of Governor Antonio Fazio,'' a source said.

   The Greens, another coalition partner, formally proposed Mr. Amato, a former Socialist prime minister, to lead the government. Mr. Amato is widely respected abroad and at home for helping Italy rein in its deficit.

   Earlier Wednesday, Mr. D'Alema rebuffed opposition calls for early elections, saying such an outcome was not automatic following the regional results.  Speaking to the upper house of Parliament, Mr. D'Alema said it was ''not fair or imperative that an electoral defeat is followed by the dissolution of the chambers'' of Parliament. He insisted that the May 21 referendum aimed at restructuring the electoral system to scrap the remaining proportional representation element had to go ahead. ''It would be paradoxical to go to a vote with a election system that all political forces regard as inadequate to guarantee government stability,'' Mr. D'Alema said.  He added that he regarded it as a point of principle to fight for the referendum to go ahead.  ''This is a problem which directly concerns the country,'' he said. ''The lack of a solution has produced a permanent instability that makes it difficult for any government to carry through its mandate to the end.'' 

   The opposition leader Silvio Berlusconi said the center-right would insist that the president call snap elections rather than appoint a new government to end the political crisis. Mr. Berlusconi, leader of the conservative Forza Italia, ruled out any possibility that the Freedom Alliance, of which Forza Italia is the main component, would go back on this demand, made since its surprise victory in the regional elections.  ''There are no valid objections'' to this request, he said at a news conference, which was also attended by Gianfranco Fini, his ally of the rightist National Alliance.  ''We will present this position to the president, which can only lead to the dissolution of the chambers and early elections,'' he said, adding  that it would be ''unacceptable to replace the prime minister by another head of government.''  Mr. Berlusconi said: ''We cannot accept this situation. There are no other ways to unblock the situation than elections.'' He said he was convinced that the center-left would be unable to agree on a successor to Mr. D'Alema.

   Leaders of parties making up the governing coalition met late Wednesday to discuss the crisis.  The Republican Party leader, Giorgio La Malfa, who used to be in the coalition, said a snap election seemed to be in the cards. ''In saying  that he's going because the center-left lost the elections, it's clear that he, too, is looking for an early general election,'' Mr. La Malfa said. 

   Financial markets have remained immune to the political maneuvering, and the employers federation, Confindustria, said Wednesday that the economy would be unaffected in the short term.  ''There is no direct impact on the growth of the country deriving from the political crisis, but rather the instability of the government makes it difficult to carry out the necessary reform program,'' Giampaolo Galli, head of Confindustria's research center, told Reuters Television. ''Therefore, in the long run, the political instability penalizes the country. But I don't expect immediate effects.''  While Mr. D'Alema prepared to quit, he also sought the best way to save the center-left from collapsing altogether.

   Consensus swelled among the center-left coalition partners to try to avoid early elections by backing a new prime minister who would be supported by Mr. Ciampi. ''We need a new prime minister, a prime minister capable of communicating with the new classes in the Country,'' said a D'Alema coalition partner, Pierluigi Castagnetti, a former Christian Democrat. ''Every time they lose, the left of yachts and fancy chefs looks at the middle classes in the north with surprised disgust,'' said a commentary in the Turin newspaper La Stampa.