JERUSALEM (Reuters) - Prime Minister Benjamin Netanyahu's tie-up with far-right coalition partner Foreign Minister Avigdor Lieberman could backfire by eroding their lead ahead of Israel's January 22 ballot, a poll said on Friday.
The findings flew in the face of Netanyahu's prediction that, by merging with his fiery rival for nationalist votes, he would muster a "big, cohesive force" of support for winning a third term as premier.
They also suggested that opposition parties, long dawdling thanks to Israel's stable economy and disillusionment with the deadlocked Palestinian peace process, would be reenergized by the conservative incumbent's new ideological tack.
According to a survey published by top-rated television station Channel Two, the joint candidate list of Netanyahu's Likud and Lieberman's Israel Beiteinu parties, announced on Thursday, would take just 33 of the 120 seats in parliament.
Though that still puts them ahead of rival parties, it represented a drop-off from Monday, before the unexpected alliance was unveiled, when a poll for parliament's television station Knesset 99 gave them a combined 39 seats.
"Unifying lists usually shrinks them," commented Nahum Barnea of the biggest-selling newspaper Yedioth Ahronoth.
"Anyone who did not tolerate Lieberman and voted for Netanyahu will think twice, and the same is true for those who did not tolerate Netanyahu and voted for Lieberman."
Friday's poll also found boosted support for Israel's strongest opposition parties, left-leaning Labour and the new, centrist Yesh Atid. They were seen taking 27 and 18 seats, respectively, up from the 19 and 15 predicted on Monday.
Reasons analysts gave for that shift included worry among wavering Israelis about the rise of Lieberman, an often undiplomatic top diplomat who faces possible indictment on graft charges - though he denies wrongdoing.
His party has sparred with Israel's Arab minority and promoted legislation that critics denounced as an undemocratic targeting of liberal causes, such as a move to slap a 45 percent tax on foreign donations to human rights groups.
While Channel Two projected an even 60-60 seat split between coalition and opposition parties in the next parliament, most commentators agreed that the latter were unlikely to build on that strength by uniting to offset the Netanyahu-Lieberman list.
"There is no agreed-upon (opposition) leader and no consensus, and almost no union seems possible there," wrote Shalom Yerushalmi of Maariv daily.
Explaining their surprise political partnership, Netanyahu and Lieberman cited the need to tackle security challenges like Iran's nuclear program and domestic problems, free of fractious small-party wrangling. The secularist Lieberman is also pushing to end en masse exemptions granted to Israeli Arabs and ultra-Orthodox Jews from compulsory national service.
Israeli media said the two leaders decided to merge after surveys commissioned by their parties predicted they would together take between 45 and 47 parliamentary seats. Sources in both parties said they were not aware of any such polls.
(This version of the story corrects the poll finding in fifth paragraph to 39 seats, from 37.)
(Editing by Crispian Balmer)