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Prime Minister Taro Aso, who triggered new elections when he dissolved the powerful lower house of Japan's parliament on Tuesday, launched his party's fight for survival with a familiar refrain: Reject change.

It's a message that has kept the ruling Liberal Democrats in power for most of the past 55 years. But Japanese voters are leaning sharply toward something new this time, and Aso's warnings about the dangers of change may not be enough to prevent a historic loss in next month's elections.

"It really looks like Japanese voters are simply fed up with the LDP," said Martin Schulz, an economist at Fujitsu Research Institute in Tokyo. "This is not just a power game right now. This is a shift in sentiment."

Aso, who had until October at the latest to disband parliament, had been under increasing pressure to exercise that power because of his dwindling support ratings and political gridlock with the opposition that has stymied business in parliament.

He had resisted calling a vote in the hope his low approval ratings would recover. He caved in after his party was routed in local elections last week and members of his own party threatened to dump him.

Hours after parliament was dissolved, Aso slammed the opposition, led by the Democratic Party of Japan, as having no substantive policies of their own and trying merely to capitalize on his unpopularity.

"We cannot leave Japan's economy in their hands," Aso said at an evening news conference. "We cannot leave Japan's security in the hands of a party without a security policy. Only the LDP can take responsibility for Japan's future."

Acknowledging the odds against him, Aso — known for his verbal gaffes — began his remarks with an apology, a bow and a promise to do better.

"The economy and protecting people's livelihoods has been my top priority," he said. "But because of my inadvertent comments, the public lost trust in me and the government. I deeply regret this."

He vowed to revive Japan's economy and suggested that a power shift now could derail an emerging yet fragile recovery.

"We're only halfway there," Aso said, noting that recent stimulus measures are starting to pay off.

Japan's central bank predicts the economy will begin climbing in the second half of this fiscal year through March 2010. But capital spending by companies is falling sharply. And private consumption, which accounts for more than half of the country's gross domestic product, remains lackluster as unemployment rises.

Analysts have predicted the elections for parliament's lower house, to be held on Aug. 30, could be disastrous for the LDP. Japan's opposition leader set the tone for the campaigns ahead, saying Tuesday the polls would be "historic."

The Liberal Democrats' near monopoly on power has enabled them to dominate the lawmaking process and select the prime minister and Cabinet members from party ranks.

Recent opinion polls show the next election could be different, with many voters saying they will defect to the opposition amid Japan's steepest recession since World War II. This has happened repeatedly in local elections, where the Liberal Democrats have suffered a string of defeats.

Democratic Party leader Yukio Hatoyama said the election would lead to a major change in Japanese politics for the first time in decades.

"This is not just a matter of drawing the curtain on the Liberal Democrats. It is not as small as that," he said. "We must go into this election with a feeling of our historic mission."

Aso is Japan's third prime minister in as many years, and with his support ratings at about 20 percent some senior members of his party have tried to oust him. Aso's decision to hold the elections was widely seen as an effort to cut his losses and give his opponents within the party less room to maneuver.

The Democrats favor a more independent stance from the U.S., smaller government and more international peacekeeping missions for Japan's military. They are also expected to try to spend their way out of the recession by funneling more money to families.

The Democrats' reputation as big spenders had been its Achilles' heel — until now.

"This has worried voters in the past. This time ... nobody expects anyone other than the government to spend money and possibly bail the economy out," said Schulz of the Fujitsu Research Institute. "The reason is, households have no money. Corporations have no money."

The leader of the party that wins the parliamentary election is almost certain to become prime minister. The Liberal Democrats have 303 seats in the powerful 480-seat lower house, and their coalition partner Komeito has 31. The Democratic Party has just 112.

The opposition controls the less powerful upper house.

Next month's elections will be the first for the lower house since 2005.