Newly elected Democratic Party of Japan President Yukio Hatoyama has a maximum of four months to convince voters to oust the party his grandfather founded from five decades of government rule.

Hatoyama, 62, was chosen president of the DPJ on Saturday, replacing Ichiro Ozawa, who quit over a campaign-funding scandal. He must win back public support damaged by Ozawa's troubles and persuade the country that a party with limited experience is best equipped to lead the world's second-largest economy out of recession.

"Hatoyama has a great opportunity to win, but you can't do that simply by being the party that's not in power," said Gerald Curtis, a professor of Japanese politics at Columbia University in New York. "It's going to be hard to climb that mountain."