The win in the Democratic Party of Japan election keeps Noda as prime minister despite low public support for his party and the likelihood he may have to dissolve the House of Representatives soon, Kyodo News reported.
Noda has expressed a willingness to reshuffle his Cabinet, reorganize party executives and work to boost the economy as the country prepares for a general election within a year.
The changes in party executives and the Cabinet could occur within the next couple of weeks, a government source told Kyodo.
Noda plans to convene an extraordinary parliamentary session in October so the government can devise a supplementary budget for fiscal year 2012 to shore up the lagging economy, officials said.
Grumblings within his party and threats of DPJ members bolting may force Noda to dissolve the House -- where his party holds a slim majority -- sooner than he wants, Kyodo said.
"If six or seven lawmakers leave the party" ending the DPJ's majority in the 480-seat chamber, "a no-confidence motion against the Cabinet could be submitted and passed," former Agriculture Minister Hirotaka Akamatsu, who challenged Noda in the leadership race, told the news agency.
Under Japan's Constitution, if the lower house passes a no-confidence motion, the Cabinet must resign unless the chamber is dissolved within 10 days of the no-confidence vote.
Kyodo said some DPJ lawmakers indicated they may leave the party and join a new party created by Osaka Mayor Toru Hashimoto.
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