Japan's Democratic Party leader Yukio Hatoyama speaks to reporters at party headquarters in Tokyo on Monday. Reuters

Likely future Japanese Prime Minister Yukio Hatoyama will soon select his cabinet, which includes a new and crucial position: a top official to take on the government's bloated bureaucracy.

Mr. Hatoyama's Democratic Party of Japan says its proposed National Strategy Bureau will set budget guidelines and other policies, wresting decisions away from government functionaries and putting them in the hands of elected leaders.

Mr. Hatoyama, fresh off his party's landslide victory in weekend elections, said late Sunday that the finance and strategy bureau jobs are among his top priorities, as the party looks for ways to finance an expensive domestic spending plan in part by cutting bureaucratic positions.

He said he would likely fill the positions this month, after he officially becomes prime minister. Speculation abounds over which DPJ officials will take the strategy bureau job and other posts. Mr. Hatoyama said Sunday it was too early to talk about his cabinet lineup.

Given the party's agenda to increase spending for families and consumers, revamping the national budget to find funds is a crucial task.

DPJ Secretary-General Katsuya Okada said Monday that when government ministries submitted budgets at the end of August as scheduled for the fiscal year beginning in April, party officials immediately began scrutinizing them. For the next fiscal year alone, the DPJ must find 7.1 trillion yen, or about $76 billion, to cover its social-spending program that includes a child allowance and elimination of highway tolls.

"This is the first hurdle we have to overcome," Mr. Okada said on public broadcaster NHK.

The party is also reviewing the 14-trillion-yen supplementary budget that departing Prime Minister Taro Aso has already implemented to cover his economic-stimulus plan with an eye toward revising it by canceling some projects.

The DPJ trounced the Liberal Democratic Party in the election for the Japanese parliament's lower house, giving it broad sway to remake the government. Final voting statistics Monday showed 72 million people, or 69% of eligible voters, participated, the highest percentage since the current voting system was enacted 13 years ago.

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The finance and strategy-bureau positions might be the most important for a future Hatoyama administration as it looks for ways to pay for its social-spending program, which could cost 16.8 trillion yen a year by the fiscal year beginning in 2013.

The DPJ campaigned on a promise it could pay for the package in part by cutting and shaking up Japan's ranks of powerful bureaucrats. "The ministries have too much power. They are more powerful than bureaucracies in other countries generally," said Kan Suzuki, vice chairman of DPJ's policy committee, in an interview.

Still, paring the bureaucracy could be a difficult task. "Politicians have been keen to cut back big government before," said one midranking bureaucrat in Kasumigaseki, the nexus of cabinet ministries in Tokyo. "I don't think there will be a revolution," the person added.

The DPJ, which has never held power in its 12-year existence, may need bureaucrats' institutional knowledge to get things done. "You're going to have a lot of new politicians who don't know their way from the prime minister's office to their own ministry making policy," said Gerald Curtis, professor of Japanese politics at Columbia University.

Japan is heavily regulated, with red tape damping all kinds of activity from setting up a business to parking a bicycle. DPJ politicians say an "iron triangle" has developed among bureaucrats, big business and the LDP, which is stifling innovation. To break up these relationships, the DPJ proposes to decentralize the bureaucracy and fill high-ranking civil-service posts with political appointments. The DPJ also has promised to outlaw the practice of "amakudari," meaning "descent from heaven," whereby government officials after retirement take up senior positions in the companies they oversaw.

An effort by former prime minister Junichiro Koizumi to centralize power recorded initial success but faltered when successive administrations lost interest.

"The DPJ needs to make sure they have the right expertise as quickly as possible because the expectations of Japanese citizens are high," said Paige Cottingham-Streater, deputy executive director of the Maureen and Mike Mansfield Foundation, a Washington-based policy organization focused on U.S.-Asia relations.

—Daisuke Wakabayashi contributed to this article.

Write to Alison Tudor at alison.tudor@wsj.com and Yuka Hayashi at yuka.hayashi@wsj.com