jerusalem | Ariel Sharon’s massive stroke has thrown Israel’s upcoming election wide open.

What looked like a foregone conclusion — with the prime minister’s Kadima Party headed toward a landslide victory — could now become a close three-way race among Kadima, Labor and Likud.

“We have an entirely different political situation: Three parties are now running toward the finish line, and no one can say who the next prime minister will be,” political analyst Sima Kadmon wrote in Yediot Achronot after Sharon was hospitalized.

Doctors remained guarded about the prognosis for the 77-year-old leader, but the stroke — Sharon’s second within three weeks — seemed likely to end the political career of a man who had outgrown his past as a polarizing figure to unite a broad swath of the public behind his plan to separate Israel from the Palestinians and set the country’s final borders.

Sharon was elected prime minister twice by huge margins and appeared poised to win another landslide in March at the head of Kadima, which he formed after leaving Likud in November. Though he was extremely overweight, Sharon was known for his energy and drive and — before suffering a mild stroke Dec. 18 — had seemed generally healthy.

Latest polls still give Kadima a huge lead, but it’s not clear how much of that support might be a fleeting sympathy vote or what will happen once the party chooses a new leader who is subjected to negative electoral campaigning by his opponents.

And there’s a deeper question: Will any successor have the political clout to continue Sharon’s policy, which could entail a significant Israeli pullback from the West Bank?

Acting Prime Minister Ehud Olmert appears to have the inside track to Kadima’s leadership, as all the party’s top people have come out in support of his candidacy. It was clear to them that a bitter fight over the succession could tear the new party apart.

The first polls taken after Sharon’s serious illness show that Kadima under Olmert would win around 40 seats in the Knesset, compared to 18 to 20 for Labor and 13 to 16 for Likud — figures similar to those forecast for Kadima under Sharon.

The early polls are significant not so much as an election forecast but because they will help Olmert consolidate his leadership position. A former Jerusalem mayor who has held numerous Cabinet posts, Olmert has been one of Sharon’s closest associates in recent years, often testing the waters by proposing controversial policies that later were seen to have come from the prime minister.

Before taking over as acting prime minister, Olmert was not the most popular figure in Kadima: He trailed ex-Laborite Shimon Peres, Justice Minister Tzipi Livni and even Defense Minister Shaul Mofaz as the people’s choice for potential successor to Sharon.

But Olmert’s still-brief term as Israel’s temporary leader already has changed that. He will hope that further incumbency strengthens his image as a national leader among Israeli voters; conversely, his opponents in Labor and Likud will hope that targeting him and focusing on his perceived weaknesses will cut Olmert down to size.

The public saw Sharon as a pragmatic centrist who could take difficult decisions and sell them to moderate right-wingers because of his security credentials. Many Israelis believed Sharon was uniquely positioned to delineate the Jewish state’s permanent borders.

Despite a reputation as a hard-liner, Sharon appeared to have undergone a profound ideological transformation in recent years and pulled Israeli settlements out of the Gaza Strip last summer, giving the Palestinians a testing ground for autonomy and creating a new window of opportunity for the peace process.

With Sharon no longer the dominant force setting the election agenda, all the leading parties are likely to build competing leadership teams.

Instead of Sharon against Labor’s Amir Peretz and Likud’s Benjamin Netanyahu, the election likely will be recast as Olmert and his team against the Peretz and Netanyahu panels.

Olmert’s team probably will include Livni and Peres. Peres said this week that acting prime minister Ehud Olmert had his full backing; in response, Olmert made Peres his deputy.

In Labor, Peretz may try to bring in former Prime Minister Ehud Barak as his No. 2 to boost his security and foreign policy credentials. He also is desperately trying to persuade Peres to return to Labor.

For his part, Olmert may well try to lure Barak, a close personal friend, to Kadima. How this post-Sharon fallout settles could decide the election.

Though he is trailing in the polls, Netanyahu cannot be ruled out altogether. As a former prime minister, he could pick up support at the expense of rivals who lack Sharon’s political heft.

On Thursday, Jan. 11, Netanyahu ordered his party’s Cabinet ministers to quit the government, a long planned move that he put off after Sharon’s stroke.

Netanyahu’s leadership ticket will include Foreign Minister Silvan Shalom, and he will try to persuade ex-Likudniks who joined Kadima to return to the fold.

Despite the wall-to-wall support Olmert seems to enjoy, he still could encounter problems within Kadima. Drawing up the party’s Knesset list could prove a minefield.

Sharon had the authority to do this more or less as he pleased, but Olmert will have to tread carefully, and will risk flak from people who feel they have been placed too low on the list.