JERUSALEM — With health on his side, Ariel Sharon was a force of nature capable of remaking Israel's political landscape again and again.

Now, clinging to life in an intensive-care unit, his political force is most likely spent.

The scramble to succeed the 77-year-old prime minister will be muted at first, out of respect for his grave condition after a massive stroke.

But when campaigning gets under way with the bare-knuckled bluster that's typical of Israel's electoral politics, the leading contenders to replace Sharon will be Benjamin Netanyahu, 56, of the Likud Party and Ehud Olmert, 60, of Kadima, the party that Sharon created late last year when he bolted Likud to escape the unyielding influence of its extreme right wing.

Labor Party leader Amir Peretz, 53, is also a contender in the early election scheduled for March 28, but analysts give his party little chance of gaining the most votes.

For the moment, under Israeli law, Olmert is serving as acting prime minister. He could hold that post for up to 100 days or until after the election. If Sharon were to die, President Moshe Katsav would have 14 days to choose an interim successor.

"Netanyahu has the inside track on winning the election and forming the government — by a narrow margin. One of the more likely outcomes is that voters who would have gone with Sharon to Kadima will be less likely to support Olmert. They will come home to Likud," said Gerald Steinberg, a professor of political studies at Bar Ilan University near Tel Aviv.

While Netanyahu, who recently won Likud's leadership primary, is the accepted head of an established party with deep roots and a party machine, Olmert sits atop a brand-new party that could prove ephemeral without Sharon.

"Olmert is going to have a lot of problems. For the first few days people will rally around the acting prime minister. But Olmert is going to have to show that he has the right stuff, and it's going to be difficult," Steinberg said.

Among Olmert's challenges are continuing rocket attacks by Palestinian militants and diplomatic choices concerning Palestinian parliamentary elections scheduled later this month. Israel hasn't yet decided whether to allow Palestinians living in East Jerusalem to vote.