JERUSALEM (AP) – A historic realignment of Israeli politics jumped forward when longtime Labor Party leader and Mideast peace advocate Shimon Peres transferred his loyalties to Ariel Sharon, a rival who turned into an ally when he pulled Israel out of Gaza.

Saying the prime minister was the best choice to lead Israel to peace with the Palestinians, Peres announced his switch on Wednesday, quitting his political home of six decades to campaign for Sharon”s new centrist party.

Peres cited peace efforts but is also piqued at Labor party members, who earlier this month rejected his bid to become Labor”s candidate for prime minister again.

Peres” defection was an important coup for Sharon in the scramble by the major parties to recruit high-profile supporters during the political realignment that has shaken the country over the past three weeks.

Now both Sharon and Peres have left parties they guided for decades, joining forces in a new political lineup. They could emerge from March 28 elections at the head of a solid bloc in favor of compromises for peace with the Palestinians for the first time.

Many Israelis respect Peres, an 82-year-old former prime minister, as an elder statesman and peacemaker, but they remain wary of his dovish politics.

His resignation from Labor could contribute to the view that he is a political opportunist. Peres also brings with him a reputation as a perennial loser at the polls who led Labor to five electoral defeats and lost a race earlier this month to lead Labor into a sixth election.

&#34This has not been an easy decision for me, but I found myself faced with the contradiction between the party of which I am a member and the requirements of the political situation,&#34 Peres said. &#34I must prefer the more urgent and greater consideration … My party activity has come to an end.&#34

Under a reported deal worked out with Sharon, Peres would support Kadima, the party Sharon formed last week after leaving the hardline Likud, but he would not officially join the party and he would not run for a seat in parliament, where he has served since 1959.

In return, Sharon would give Peres a senior post in his next government if Sharon is re-elected. His voice shaking with emotion, Peres said the decision to leave Labor was not easy, but he believed Sharon was best suited to pursue a peace deal with the Palestinians.

&#34I am convinced that he is determined, as I am, to continue with the peace process and restart it immediately after the elections,&#34 he said. &#34I decided, therefore, to support his election and cooperate with him to realize these goals.&#34

Peres” critics said he was more concerned with remaining at the center of Israeli politics than with ending the Mideast conflict.

&#34You can present everything as a principle … The peace process is important, but more important is, ”Where do I stand with the peace process? Is peace being done without me?”&#34 Shlomo Ben-Ami, a one-time Labor foreign minister, told The Associated Press.

Despite their political differences, Peres and Sharon forged a friendship over the decades which they turned into a political partnership in recent years as Sharon fought attempts by Likud hard-liners to torpedo his Gaza withdrawal plan. Sharon has said Israel would have to leave parts of the West Bank, while maintaining major settlement blocs, in any final peace deal with the Palestinians.

Peres is feted abroad as a statesman and shared the 1994 Nobel Peace Prize with Prime Minister Yitzhak Rabin and Palestinian leader Yasser Arafat.

But at home, he is renowned for his multiple electoral defeats. He served three brief stints as prime minister, twice replacing Rabin and once as part of a rotation agreement with a hardline rival after a deadlocked election. He also lost a surprising parliamentary vote for the country”s ceremonial president, an office that would have given him a dignified exit from politics.

In another shocking defeat, this month Peres lost the Labor Party primary to union leader Amir Peretz, who immediately began working to rejuvenate the floundering party, recruiting academics, a prominent journalist and a reclusive millionaire to join its parliamentary slate.

Peretz” moves appear to be working, according to a series of favorable polls.