Ariel Sharon's massive stroke threw Israeli politics and Mideast peacemaking efforts into turmoil, threatening momentum for a deal with the Palestinians and enhancing the position of hard-liners.

The Israeli prime minister broke away from the Likud Party of Benjamin Netanyahu in November, and the new centrist party he formed had been the favorite to win March 28 elections. But Kadima was largely a one-man show which would have an uncertain future without the 77-year-old Sharon.

Medical experts said the chances are slim for Sharon to make a full recovery from the sort of massive stroke he suffered Wednesday.

In recent months, many Israelis have placed high hopes on Sharon as the politician best positioned to draw Israel's final borders in a settlement with the Palestinians.

The prime minister — once his country's foremost champion of Jewish settlement-building in the West Bank and Gaza — in September became the first Israeli leader to relinquish land the Palestinians claim for a future state when he led Israel out of the Gaza Strip.

Sharon's transformation from hawk to pragmatist — combined with last year's death of longtime Palestinian leader Yasser Arafat — has given the Middle East a chance for a return to peacemaking after five years of relentless bloodshed.

In March, Sharon had been expected to face off against Netanyahu, the tough-talking former prime minister who recently won the Likud primaries, and Amir Peretz, the union leader who recently unseated veteran Israeli politician Shimon Peres as head of the liberal Labor Party.

None of Sharon's possible successors were seen as having his ability to pull together the next ruling coalition.

Sharon's deputy, former Jerusalem mayor Ehud Olmert, has already taken over the reins of power after the stroke and could emerge as Sharon's successor heading the Kadima, or Forward, party.

Olmert, although a familiar face in Israeli politics, would likely have a far tougher time beating either Netanyahu or Peretz than Sharon would have.

After losing to Peretz in the Labor primaries, Peres, a Nobel Peace Prize laureate, joined Sharon in Kadima, and it was not clear if he would seek leadership of the new party. The 82-year-old Peres, though serving briefly as prime minister three times, has never won an Israeli election outright and lost to Netanyahu in 1996.

At the time of his stroke, Sharon was still in the process of coming up with a list of candidates to run under the Kadima banner. Now both Kadima's parliamentary lineup and its electoral future have been thrown into question.

Sharon had indicated that he expected significant progress toward peacemaking in 2006, despite continued violence and growing chaos in the Palestinian territories. Nonetheless, no major peace moves had been expected until after the Israeli elections in March and Palestinian parliamentary elections scheduled for Jan. 25.

Though Sharon made history by pulling Israeli troops and civilians out of the Gaza Strip and part of the West Bank, most Palestinians regard the ex-general as an enemy because of his bloody military campaigns against Palestinian guerrillas in Lebanon, Jordan and elsewhere.

Sharon's exit from the political stage would scramble Israeli politics but also redraw personal relations that are key to Mideast diplomacy.

Sharon and President Bush forged close ties after a rough beginning and the Israeli leader has been a frequent visitor at the White House. Bush warmly embraced Sharon's withdrawal from Gaza and backed his tough policy against Palestinian militants, echoing Sharon's demand that the Palestinians take steps to stop attacks on Israel.