On Thursday a third survey showed Sharon, at odds with Netanyahu over the withdrawal from Gaza, would easily win a general election on the back of support for this month's pullout if he broke with Likud and formed his own centrist party.
The Likud Central Committee, which opposed the pullout for defying the party's rightist ideology, votes on Monday on Netanyahu's motion to advance a leadership primary to November, when he would challenge the former general.
A poll broadcast by Channel 10 television gave Netanyahu's supporters 46.5% to 44.5% for Sharon's allies.
An earlier poll in the Haaretz daily showed 45.5% of the 3000 committee members favour an early primary, against 40.3% who want it staged in April as scheduled.
Netanyahu was opposed to the
pullout from Gaza
But 11.5% of those questioned for Haaretz said they had no opinion and 2.7% declined to answer, indicating the contest was too close to call.
Israel's next election is due in November 2006. An early primary would almost certainly bring it forward by undermining the tactical coalition Sharon forged with the centre-left Labour party to get the Gaza plan past Likud rebels.
A win for Sharon on Monday would derail the challenge from Netanyahu. If Sharon loses only narrowly, he could hang on to see if polls shift his way ahead of the primary - a possibility if Palestinian fighters stick to a truce and Israeli rightist anger over the pullout fades.
If Sharon is routed by Netanyahu, political analysts predict he would quickly break away from Likud to take advantage of cross-party support for his policy of "disengagement" from
conflict with the Palestinians.
A survey in the biggest daily Yedioth Ahronoth daily found Sharon would win 36 parliamentary seats in a general election at the head of a new party, only four fewer than Likud has now. It gave Labour 16 seats and only 14 to a Netanyahu-led Likud.
Netanyahu was unimpressed. "Let the polls give him 400 seats, it has no meaning," he told Israel Radio. "When parties split with no real path ... they end up with nothing."
Netanyahu began a quest to remove Sharon as Likud leader after quitting as finance minister in August to protest at the Gaza pullout and the removal of all Jewish settlements there.