By Dan Williams
JERUSALEM, March 18 (Reuters) - Embarrassed at failing to predict Prime Minister Benjamin Netanyahu's election victory, Israeli pollsters said on Wednesday they were blindsided by reticent rightist voters and may have unwittingly prodded waverers to back the incumbent.
Netanyahu's Likud won 30 of parliament's 120 seats in Tuesday's ballot, against 24 for the center-left Zionist Union - upsetting opinion surveys that as recently as Friday gave the challenger a four-seat lead.
Exit polls also proved unreliable. Israel's top three television stations, airing first returns as voting booths closed, found the parties close or tied. Had that been borne out, either could have potentially headed the next government.
Instead, during overnight counting, Likud's tally went from 27 seats to 30 and the Zionist Union's from 27 to 24.
Grilled on the discrepancy, Channel 2 TV's veteran pollster Mina Tzemach said many Likud voters declined to take part in replicating their vote in the dummy ballot boxes set up by survey-taking companies outside voting stations.
Even though exit polls are anonymous, she suggested such reticence might have cultural roots for Israelis originally from countries with different political regimes in which they worry about sharing their private voting choices.
"In certain voting stations, voting stations in places where there are a lot of new immigrants, pro-Likud ballot boxes, the percent of those who voted (in the exit polls) was especially low," Tzemach told Israel's Army Radio.
Fellow survey-taker Camil Fuchs agreed, saying final counts from voting stations he had monitored showed that a significant number of Likud supporters had not participated in exit polls.
If they did participate, they may also not have been honest about the way they voted and as exit polls close earlier than the real polls, a last-minute surge in Likud votes, in response to a call from Netanyahu, may have been missed, he said.
"Some people don't say (in exit polls) what they really voted, and the exit polls close about two hours before the voting booths," Fuchs told Israel Radio.
Israeli election forecasts have been wrong before - in 1981, when the Likud narrowly won; in 1992 about the return to left-wing Labor party rule; and in 1996, when Netanyahu toppled Labor incumbent Shimon Peres for his first term in office.
Recent reliance on Internet-based studies has thrown another spanner in the works, according to Avi Degani, an Israeli pollster who says he conducted telephone surveys exclusively. Since last month, he has been the only one consistently predicting a victory for Netanyahu.
Degani said Web-based "panels," made up of tens of thousands of pre-selected respondents, rarely reflect Israeli society accurately as they favor the tech-savvy, educated and urbane.
"The Internet does not represent the State of Israel or the people of Israel. (It is) biased strongly toward Tel Aviv," Degani told reporters in a conference call arranged by the Israel Project advocacy group, referring to Israel's second largest city and financial capital.
"People who are in the periphery ... and have a stronger tendency to vote Likud are, I think, very poorly represented."
In separate remarks to Reuters, Degani said Israeli pollsters were always bedeviled by some 30 percent of citizens whose votes are unknowable - either because they waver until the last minute or end up backing fringe parties that do not muster enough support to enter parliament and are nixed from the tally.
"We are talking about 20 parliament seats that could go either way. It is almost impossible to tackle statistically."
Still, Degani said he anticipated Netanyahu's win by finding that at least half of wavering voters would choose Likud, adding that some of those respondents viewed themselves as rallying against Zionist Union's strong showing in opinion polls.
"It is a highly emotional matter in Israel, and the Likud had the added advantage of being the last party, with the possible exception of (liberal) Meretz, of having a defined ideology. The rest are just about personalities," Degani said. (Writing by Dan Williams; editing by Anna Willard)