Israeli Prime Minister Ariel Sharon has decided to leave the Likud Party he helped found more than three decades ago and lead a new political movement into the next elections, according to Israeli news reports and an aide familiar with the decision.

Sharon, 77, is expected to announce his departure Monday after meeting with President Moshe Katsav, whom he will ask to dissolve parliament. Sharon made the decision late Sunday after meeting with advisers and party members throughout the day, the aide and news reports said.

The aide, who spoke on condition of anonymity because he is not authorized to comment publicly about the decision, said 12 to 16 Likud members of parliament will also leave the party and start what will probably be a moderate political movement. Likud, traditionally hawkish on issues of peace with the Palestinians, controls 40 seats in the 120-seat parliament.

"He said it was the most difficult decision of his political career," the aide said, referring to conversations Sharon had with party members during the day.

Sharon's departure would accelerate the realignment of Israeli politics along ideological and generational lines.

He helped found Likud 32 years ago but alienated much of its hawkish base by evacuating Israeli soldiers and settlers from the Gaza Strip this year. Although broadly popular with the Israeli public, he faces organized opposition for the right to lead Likud into the next elections, likely to be held next spring.

Last week, several of Sharon's political advisers said he would probably be elected prime minister for a third time at the head of Likud, an assertion recent opinion polls corroborate. But they said he feared party dissidents would block any future efforts he might make to end the conflict with the Palestinians.

Earlier on Sunday, the Labor Party, Sharon's main coalition partner for nearly a year, voted to withdraw its eight ministers from the cabinet, as expected. Amir Peretz, the longtime labor union leader who won the Nov. 10 party leadership vote, had promised to leave the government and trigger early elections.

Peretz, 54, told the Labor central committee that Sharon had "humiliated" his party's members by embracing an economic policy of lower public spending and privatization.

"Come join the new social pact," Peretz said in a full-throated speech, reaching out to disaffected Likud voters. "You are not abandoning Likud. Likud has abandoned you."

On Sunday, Sharon told Shimon Peres, 82, who lost the recent Labor leadership vote, that he would soon need his services. Political analysts have suggested that the two men, who have been active in Israeli public life for six decades, could win over many moderate voters if they formed a party focused on ending the conflict with the Palestinians.

Israeli Prime Minister Ariel Sharon helped to establish Likud.