Japan's main opposition Democratic Party looks set to win an election on Sunday by a huge margin and could even secure a two-thirds majority in parliament's powerful lower house, a newspaper survey showed on Thursday.

An opposition victory would end more than 50 years of almost unbroken rule by the conservative Liberal Democratic Party (LDP) and break a policy deadlock caused by a divided parliament, where the opposition controls the upper house and can delay bills.

Yukio Hatoyama's Democrats have promised to focus spending on households, cut waste and wrest control of policy from the hands of bureaucrats. But their pledge to keep the sales tax at its current 5 percent for the next four years has raised concerns about further inflating Japan's already huge public debt.

Previous surveys have already shown the Democrats are on track for a runaway win over Prime Minister Taro Aso's LDP, which has ruled the country for all but 10 months since its founding in 1955, but the Asahi newspaper said that an even bigger victory was within sight.

A two-thirds majority in the lower house would allow the chamber to enact bills rejected by the upper house.

That is unlikely to be an immediate necessity for the Democrats, since they and small allies control the upper house now, but it would allow them to push through laws even if the LDP and its partner win an upper house election set for mid-2010.

Analysts have cautioned that much of the trend is due to anger at the LDP over scandals, policy flip-flops and a perceived inability to solve the deep problems of Japan's fast-aging society rather than enthusiasm for the decade-old Democrats.

Rather than supporting the Democrats because they think their policies are good, the biggest factor is the negative evaluation of the LDP's performance, said Kazuhisa Kawakami, a political science professor at Meiji Gakuin University.

Investors in Japan's stock market would generally welcome an end to the parliamentary deadlock, but share prices may already have factored in a Democratic Party win.

The Asahi said some 30-40 percent of voters had not revealed their preference so the results could alter, and analysts have said forecasts of a landslide could scare away some voters.

But analysts said the tide was unlikely to turn in the LDP's favor at this late stage. It is not a situation where undecided voters would rush to vote for the LDP, as they still have negative feelings about Mr. Aso and the party. The LDP has yet to send out a message that could revive itself, Kawakami said.

Democratic Party leaders have warned against complacency, and party leader Hatoyama -- now looking likely to be Japan's next prime minister -- sought to reassure voters that the party would not abuse its power if it wins big.

If we take power, we will of course create a government that takes account of your feelings. We won't forcibly decide things using the law of numbers, so please don't worry, Hatoyama said in a campaign speech in western Japan on Wednesday.

Struggling Prime Minister Aso, who has attacked the Democrats as weak on security and fuzzy on how to fund its spending programs, sought to highlight the risk of change.

Politics is not gambling, he told a crowd this week.

Japan