Despite a congratulatory call from Prime Minister Olmert, Foreign Minister Tzipi Livni’s margin of victory in last night’s primary vote may prove too thin to ensure her immediate ascension to Israeli prime minister.

A count of the ballots from polling stations across Israel showed that projections made shortly after the polls closed gave much too wide a margin for Ms. Livni over her nearest rival for the leadership of the ruling Kadima Party, Transportation Minister Shaul Mofaz.

“The good guys won,” Ms. Livni, 50, told supporters, after exit polls showed that she had won as much as 49% of the vote and that Mr. Mofaz had received 38%, with two other competitors in the single digits. Later, however, sources at Ms. Livni’s campaign headquarters told Israeli press outlets that her margin of victory over Mr. Mofaz could be as slim as 2%.

Mr. Mofaz is expected to contest the count, and a runoff vote could be held next week.

Even if Ms. Livni, a relatively new political star in Israel, emerges as the victor in the contest for her party’s leadership, her road to the premiership could prove difficult, and a general election could be called for as soon as February or March. Recent national polls show that Ms. Livni is lagging far behind the leader of the right-of-center Likud Party, Benjamin Netanyahu; Likud spokesman said last night that they have no intention of joining a coalition led by Ms. Livni.

If Ms. Livni fails to put together a coalition, the current cabinet could become a caretaker government headed by Mr. Olmert, who is expected to resign soon after a new party leader is chosen. Such a government would remain in power until a general election can be held.

A strong believer in Kadima, which Prime Minister Sharon founded in 2005 to fill a void in the political center, Ms. Livni increasingly is seen as an alternative to Israel’s traditional politicians. Israelis view her as untainted by personal corruption, in contrast to Mr. Olmert, who is the target of several criminal investigations. “Livni is straight as an arrow,” a veteran columnist for Haaretz, Yoel Marcus, wrote earlier this week. She “projects the image of an honest person with moral brakes.”

Mr. Mofaz, an Iranian-born former army chief of staff and defense minister, has run on his strong military credentials, which he says best positions him to deal with the Iranian nuclear threat. Ms. Livni instead highlights the agreements she has made with the Palestinian Arabs. That tack, however, has put her at odds with at least one current coalition partner, the fervently Orthodox Shas Party. The leader of Shas, Eli Yishai, said yesterday that he would join a new coalition only if promised that Jerusalem would remain united under Jewish rule, a sensitive component of any agreement with the Palestinian Arabs.

Without his party, Mr. Yishai said, any coalition would fold quickly, leading to general elections. Unless she pacifies Shas, Ms. Livni will have to rely on Labor and several small parties, including the far left Mertez and some anti-Zionist Arab parties, to form a government that would survive a no-confidence vote by 61 legislators in the 120-member Knesset.

As soon as Mr. Olmert’s resignation takes effect, President Peres is expected to consult with a likely candidate to lead a government, giving him or her 42 days to put together a coalition. If no candidate succeeds, a general election will take place within 90 days. If Ms. Livni gets enough support, however, she does not have to call an election for two years. She would then be better positioned to win, running on her own record as the country’s only female leader since Golda Meir, than now, as a senior member of the extremely unpopular Olmert government.