Jerusalem ? Once Israel’s premier hawk, Ariel Sharon has undergone a startling transformation over the past two years.

He pulled Israel out of the Gaza Strip this summer and uprooted Jewish settlements he once backed, fighting off challenges from within his own Likud Party.

Sharon’s final break with the hard-liners came on Monday: The 77-year-old premier announced he would quit Likud and form a new centrist party so he would be free to pursue new peace efforts with the Palestinians.

In so doing, he became the first sitting prime minister in Israeli history to break away from his party. The move electrified Israeli politics and sets the stage for likely March elections.

The Gaza pullout created a “historic opportunity,” Sharon told a televised news conference. “I will not allow anyone to squander it.”

Palestinians said the developments created new prospects for peacemaking, which ground to a halt during five years of violence.

“I believe this is an eruption of an Israeli political volcano, and I hope that when the dust settles, we will have a partner in Israel to go toward … a final arrangement,” said Palestinian negotiator Saeb Erekat.

Israeli Prime Minister Ariel Sharon speaks during a press conference Monday at his Jerusalem office. Sharon broke away from his hardline Likud Party to form a new centrist party.

Sharon ruled out unilateral withdrawals from the West Bank, however. He said he remains committed to the internationally backed “road map” plan, which calls for a negotiated peace deal culminating in a Palestinian state.

Weekend polls indicated Sharon, Israel’s most popular politician, could marshal enough support to return to the prime minister’s office for a third term at the head of a moderate coalition.

Sharon said he turned his back on former Likud allies who opposed his Gaza withdrawal because life within the party had become “insufferable.”

“The Likud in its present configuration cannot lead the nation to its goals,” Sharon said.

Sharon set dramatic events in motion late Sunday with his decision to leave the party he co-founded more than 30 years ago.

On Monday, Sharon went to President Moshe Katsav to ask him to dissolve parliament, the Knesset, and move up elections to early March from their scheduled November date.

Katsav has yet to declare whether he would disband the legislature or let parliament dissolve itself.