As Israel’s election campaign begins in earnest on Tuesday with a two-week blitz of television ads, Prime MinisterBenjamin Netanyahu is battling a problem that, at first glance, may seem enviable: Everyone seems sure that he will win.

In Israel’s multiparty, coalition system of government, that presumption has led many of Mr. Netanyahu’s traditional supporters to flirt with smaller parties that cater to special interests.

A whopping 81 percent of survey respondents expect him to serve another term, according to a poll conducted by Dialog and published last month in the newspaper Haaretz. Yet surveys ever since have shown that support is slipping for the joint list of candidates Mr. Netanyahu heads, from its current 42 of Parliament’s 120 seats to as few as 32.

“That’s the danger of being a front-runner: When everyone assumes he’s going to win, they feel like they have the luxury of voting their real ideology,” said Gadi Wolfsfeld, a professor of political communication at the Interdisciplinary Center in Herzliya. “Ironically, what he’s trying to do is prove that the left really could win. If he can somehow undermine that certainty that he’s going to win, then of course he has a realistic chance of bringing some votes back.”

Political analysts and some people inside the campaign say that this challenge has been compounded by a lackluster campaign, infighting and a series of strategic errors that include criticizing other conservatives. Although Mr. Netanyahu is still the favorite to form the next government, experts predict he could end up with a relatively slim majority in Parliament rather than a broad unity coalition that would give him freer rein to set policy and define his legacy.

“Somewhere between disastrous and catastrophic” is how Sam Lehman-Wilzig, deputy director of the school of communication at Bar-Ilan University, described the incumbent’s campaign so far. “There’s no ‘there’ there. It’s a pure emotional ‘we don’t want the left in power’ and ‘trust me’ and ‘I have experience and that’s why you should vote for me.’ I don’t think that’s going to enthuse a lot of people.”

Mr. Netanyahu’s allies and campaign aides acknowledge that the last month has been rocky, but they said the next two weeks would be what matters. “The only poll that we are looking at is the election results on Jan. 22,” said one senior official, promising a “much more focused messages in the homestretch.”

Critics say the first major mistake was the decision to merge Mr. Netanyahu’s Likud Party with the ultranationalist Yisrael Beiteinu. That, combined with a Likud primary that ousted several popular moderates, alienated some centrist voters, the analysts said. Then, as right-wingers flocked to Naftali Bennett, the charismatic young leader of the new Jewish Home party, Mr. Netanyahu attacked him as well as the ultra-Orthodox Shas Party, a longtime political partner. Both attacks seem to have backfired.

Some analysts and people inside Likud-Beiteinu complain that the prime minister has been too quiet and reactive, and that his recent push on Jewish settlements in East Jerusalem and the West Bank put the Palestinian conflict at the center of the campaign, forcing the Iranian nuclear threat, on which he is stronger, into the background.

In most of these cases, “you can see the fingerprints of Finkelstein,” said Gabriel Weimann, a professor at the University of Haifa who specializes in political communication, referring to the American political consultant Arthur Finkelstein. “Finkelstein is running the campaign. People in his own party were criticizing Netanyahu for following Finkelstein when he is sitting in the States and doesn’t know what’s happening here.”

Mr. Finkelstein, a Republican strategist from Westchester County, N.Y., who has run many hard-edged conservative campaigns in the United States and Israel, including Mr. Netanyahu’s for his first term as prime minister in 1996, declined through campaign aides to be interviewed. He was summoned to Jerusalem last week as the campaign was flailing, and several analysts and insiders say they can already see the beginning of a shift in strategy.

For one, the attacks on Mr. Bennett have ceased. And the prime minister seems to be lightening up: he made a big show of wearing jeans to a young professionals’ campaign event here Sunday night, and he was warm and personable in an interview broadcast Monday night, sitting in his childhood home as he recalled playing ball and roasting potatoes with his brothers.