For Mr. Netanyahu, who entered the race an overwhelming favorite with no obvious challenger, the outcome was a humbling rebuke as his ticket lost seats in the new Parliament. Over all, his conservative team came in first, but it was the center, led by the political novice Yair Lapid, 49, that emerged newly invigorated, suggesting that at the very least Israel’s rightward tilt may be stalled.

Mr. Lapid, a telegenic celebrity whose father made a splash with his own short-lived centrist party a decade ago, ran a campaign that resonated with the middle class. His signature issue is a call to integrate the ultra-Orthodox into the army and the work force.

Perhaps as important, he also avoided antagonizing the right, having not emphasized traditional issues of the left, like the peace process. Like a large majority of the Israeli public, he supports a two-state solution to the Israeli-Palestinian conflict, but is skeptical of the Palestinianleadership’s willingness to negotiate seriously; he has called for a return to peace talks but has not made it a priority.

Sensing his message of strength was not penetrating, Mr. Netanyahu posted a panicky message on Facebook before the polls closed, saying, “The Likud government is in danger, go vote for us for the sake of the country’s future.” Tuesday ended with Mr. Netanyahu reaching out again — this time to Mr. Lapid, Israel’s newest kingmaker, offering to work with him as part of the “broadest coalition possible.”

Israel’s political hierarchy is only partly determined during an election. The next stage, when factions try to build a majority coalition, decides who will govern, how they will govern and for how long. While Mr. Lapid has signaled a willingness to work with Mr. Netanyahu, the ultimate coalition may bring together parties with such different ideologies and agendas that the result is paralysis.

Still, for the center, it was a time of celebration.

“The citizens of Israel today said no to politics of fear and hatred,” Mr. Lapid told an upscale crowd of supporters who had welcomed him with drums, dancing and popping Champagne corks. “They said no to the possibility that we might splinter off into sectors, and groups and tribes and narrow interest groups. They said no to extremists, and they said no to antidemocratic behavior.”

With 90 percent of the vote counted, Israel Radio reported Wednesday that Mr. Netanyahu’s conservative Likud-Beiteinu ticket was poised to take 31 of Parliament’s 120 seats. Mr. Lapid’s party, Yesh Atid — There Is a Future — garnered 19, many more than polls had predicted.

The right-wing and religious parties that make up Mr. Netanyahu’s current coalition combined for 60 seats, according to Israel Radio, equal to the total won by the center, left and Arab parties, pushing the prime minister toward a partnership with Mr. Lapid and perhaps some of the groups that had been in the opposition. The left-leaning Labor Party took 15 seats and Jewish Home, a new religious-nationalist party, 11.

The prime minister called Mr. Lapid shortly after the polls closed at 10 p.m. Tuesday and, according to Israeli television reports, told him that they had great things to do together for the country. In his speech to a rowdy crowd of supporters here Wednesday morning, he said, “I see many partners.”

Mr. Lapid indicated he was open to working with Mr. Netanyahu, saying the only way to face Israel’s challenges was “together.” But he added: “What is good for Israel is not in the possession of the right, and nor is it in the possession of the left. It lies in the possibility of creating here a real and decent center.”

The results were a blow to the prime minister, whose aggressive push to expand Jewish settlements in East Jerusalem and the West Bank has led to international condemnation and strained relations with Washington. The support for Mr. Lapid and Labor showed voters responded strongly to an emphasis on domestic, socioeconomic issues that brought 500,000 people to the streets of Tel Aviv in the summer of 2011.