The DPJ leader, 62-year-old Yukio Hatoyama, will almost surely assume the position of prime minister in a special parliamentary session in September. His party’s win in the Sunday elections ends 55 years of almost continuous rule by the conservative LDP.

Analysts view the DPJ victory as a rejection by Japanese voters of the LDP’s fumbling of the economy rather than an embrace of the DPJ’s politics.

The DPJ, made up of a hodgepodge of defectors from opposition parties, must act quickly to show voters it can do better than its more experienced rival. The DPJ won control of the upper house in 2008 elections, so it will have a smooth ride in pushing its agenda through parliament. It has less than a year before its mandate will be challenged in upper house elections, however.

Hatoyama, one of the founding members of the DPJ, began setting up his Cabinet Monday. His priority is the search for a competent finance minister.

In the lead-up to the election the LDP, which was formed in 1955, reminded voters that it had led the country out of its postwar doldrums and raised Japan to economic superpower status. It did this by allying with big business and conservative interest groups.

But Japan’s big companies can no longer guarantee lifelong employment to huge sections of the workforce. Now, with the country hit hard by recession, unemployment has hit a record 5.7 percent.

The DPJ promised voters it would not raise the 5 percent sales tax for four years. It has other proposals, too. In view of the declining birthrate, which is expected to draw Japan’s population of 127.6 million down to less than100 million by 2050, the party plans to hand out $275 per month per child to encourage women to have more babies.

Toll-free highways, free high schools, support for farmers and monthly allowances for workers in training, a higher minimum wage and tax cuts are also on the planning board. Critics say that these plans, which could cost up to $179 billion, will further bloat Japan’s massive debt.

For the United States, the DPJ victory may mean a shift in relations between Tokyo and Washington. Japan, under the right-leaning LDP rule, has consistently been a strong U.S. ally but the DPJ has indicated that it wishes to be more independent of Washington and to strengthen ties with its Asian neighbors.

Edward J. Lincoln, director of the Center for Japan-U.S. Business and Economic Studies, said: "There is nothing that is more important in Asia than maintaining good relations with Japan and China; they are the two big powers. And there has been a legacy of bad feeling between Japan and Korea stemming from the colonial period in the first half of the 20th century. If they can take some positive steps in these issues, it would be most welcome."

However, it is unlikely that Hatoyama’s government will take steps to seriously alienate its closest ally, especially with the economic and military rise of China a growing concern.

"One of the most important things for any Japanese government is to show to the electorate that they can manage the U.S.-Japan relationship well and that includes the security relationship," Lincoln, speaking at the Japan Society a few week ago, said. "So they’re really not in the position to do things that fundamentally irritate the United States."