TOKYO (Reuters) - Nearly two-thirds of Japanese voters don't understand why Prime Minister Shinzo Abe is calling a snap election next month and about half want ruling and opposition parties to come out evenly in the poll, a survey showed on Thursday, suggesting Mr Abe's ruling party might fare less well than he hopes.

Mr Abe, who returned to power when his Liberal Democratic Party (LDP) crushed the then-ruling Democratic Party of Japan (DPJ) in a December 2012 election, said on Tuesday he would postpone an unpopular sales tax hike slated for next October and call a snap election to seek a fresh mandate for his "Abenomics" strategy .

Just over 63 per cent did not understand why Mr Abe was calling the election now, a Kyodo news agency survey on Nov 18 to Nov 19 showed. No general election need be held until late 2016, but Mr Abe hopes to cement his grip on power while the opposition is weak and before his relatively robust support rates slide.

Mr Abe took office pledging to reboot Japan's economy with hyper-easy monetary policy, spending and reform. But data released on Monday showed the economy slipped into recession in the third quarter as an April sales tax hike to 8 per cent hit consumption. A second rise to 10 per cent had been set for October 2015 as part of plans to curb Japan's huge public debt.

The Kyodo survey showed 25.3 per cent of voters planned to cast ballots for the LDP in proportional representation districts, far more than the 9.4 per cent who favour the DPJ.

But 44.4 per cent were undecided, while about half said they hoped that the ruling and opposition parties would end up evenly matched in the powerful chamber after the election.

Mr Abe has said he would resign if his coalition - which holds two-thirds of the Lower House seats - fails to win a simple majority, an outcome experts dismissed as almost impossible.

But Mr Abe could end up weakened if the LDP loses too many seats. "If they lose more than 30 to 40 seats, he won't be forced out of office, but he will be badly wounded and might face a difficult situation when he seeks another (LDP) term in September," said Columbia University professor Gerry Curtis.

"But the most likely scenario is that, thanks to the inability of the opposition parties to cooperate, even as the LDP vote decreases, they come up with a strong majority," he added.