TOKYO (AFP) –
Japan's Prime Minister Taro Aso on Thursday admitted voters were unhappy with his party's performance ahead of a weekend election as a survey showed the main opposition was set for a landslide win.

The untested centre-left Democratic Party of Japan (DPJ) could win as many as 320 seats in the 480-seat lower chamber on Sunday, the Asahi Shimbun newspaper predicted after quizzing more than 130,000 voters.

Following more than half a century of almost unbroken rule, Aso's Liberal Democratic Party (LDP) "looks certain to suffer a crushing defeat" and could be left with as few as 100 seats, down from 300, the daily said.

"I think criticism has been building" toward the conservative government, the embattled premier said while campaigning in the western city of Osaka, Jiji Press news agency reported.

"We have failed to make clear the virtues of conservatism," he said. "We regret we haven't sent a clear message in the past few years."

The DPJ already controls the upper house with the help of smaller parties.

The Asahi, which conducted its telephone poll over four days to Tuesday, said it had factored in past election results and other information from its nationwide reporters' network in making its predictions.

But the daily warned that the situation could change, with nearly 40 percent of respondents saying they were undecided or declining to say which party they would vote for in 300 single-seat constituencies.

Voting decisions were also unclear for 30 percent of respondents in the proportional representation section of the ballot, which distributes 180 seats.

Finance Minister Kaoru Yosano on Tuesday acknowledged the DPJ is likely to win be a landslide and warned it could create a "one-party dictatorship".

DPJ leader Yukio Hatoyama later refuted the claim, arguing that his centre-left party would take a conciliatory approach.

"Which party has used the two-thirds and ignored people's voices?" he said on a stumping tour in western Japan Wednesday, in an apparent stab at the LDP-led coalition government, according to local media.

"If we come to power, we will avoid deciding everything by force with the power of having the numbers," he said.

The LDP, with the Buddhist-backed New Komeito party, commanded a two-thirds majority in the lower house dissolved last month, which allowed it to override the opposition-held upper house and push through laws.

Aso, for his part, has mounted attacks against the buoyant opposition, charging it had never managed a government before and arguing the DPJ's spending pledges amounted to "free-spending socialism".

With looming prospects of a big DPJ victory, speculation is already rife about the cabinet line-up under Hatoyama.

The Kyodo News agency has reported that a top candidate for finance minister was Hirohisa Fujii, 77, already a top adviser to the DPJ.

Fujii served in the post in two short-lived governments in 1993-94, the only period since 1955 in which the LDP was out of power.

Some DPJ members have said party secretary general Katsuya Okada, a former trade ministry bureaucrat, should become finance minister, Kyodo said.

The Sankei Shimbun has said Okada may become foreign minister.