Israeli exit polls forecast a slim victory on Tuesday for the centre-left Kadima party of Foreign Minister Tzipi Livni, but the margin may be too narrow to ensure she becomes prime minister.
The polls gave Kadima a two-seat lead over Benjamin Netanyahu's right-wing Likud party in the contest for parliament's 120 seats.
But when the projected results are broken down into left and right-wing blocs in parliament, Likud under the hawkish Netanyahu, a former prime minister, appeared best positioned to put together an administration.
According to the poll forecasts after voting ended, Kadima and left-wing parties would command only 56 seats in parliament, short of a majority, while a right-wing bloc would control 64, enough to govern.
Israel's president traditionally delegates the task of forming a coalition government to the leader of the party that wins the most parliamentary seats, but he can also choose any legislator he decides has the best chance of doing so.
President Shimon Peres is likely to hold consultations later this week with the leaders of political parties, after the final election results are in.
Once he asks a legislator to form a government, he or she has up to 42 days to do so. Should coalition talks fail, Peres can ask another legislator to assume the task.