Miller's resignation was in the works for some weeks now. Members of his Democratic Left Alliance (SLD) had been waging an open mutiny after Miller's popularity plunged because of unpopular social reforms and scandals. In early March, he stepped back from the leadership of the SLD, the successor to Poland's communist party. On Friday, he took the final step.

"If my resignation should help Poland and the Polish left, then my decision is to give up the leadership of the government," Miller told reporters Friday evening.

His decision to step down came after more than 25 parliamentarians made good on their threat to defect from the SLD to form their own social democratic party. Polish President Aleksander Kwasnieswki accepted Miller's decision and said he would propose a successor on Monday. In line is former prime minister and deputy premier Jozef Olesky.

"A change of prime minister and a government reconstruction are necessary," said parliament speaker Marek Borowski, one of the defectors, according to the Associated Press.

Beset by scandals, high unemployment

The announcement marked the final phase of what has been a rocky road for Miller, 57, since he wrestled power away from the conservatives in 2001 by winning 42 percent of the vote. He rode a wave of measured optimism, winning points by aggressively negotiating Poland's entry into the European Union. His decision to support the United States with special forces troops and military aid during the Iraq invasion was less popular, though many Poles delighted in the attention and praise lavished upon them by Washington.

But his government was beset by scandals. Chief among them, the revelation that a film producer allegedly offered a bribe to the bosses of Poland's largest media corporation on the suggestion of some high-ranking government officials. High unemployment and unpopular reforms in the country's social system led to approval ratings that hovered around 9 percent in recent weeks.

The SLD "lost 4.5 million voters within two and a half years," said Borowski, who now belongs to the newly-established Polish Social Democracy party. The party plans to field candidates for the European Parliament elections in June.