Japan's prime minister began replacing his four-month-old Cabinet on Friday in an attempt to revive the struggling economy and expand free trade to keep the country globally competitive.

Prime Minister Naoto Kan said the new Cabinet is aimed at pushing for legislative reforms to address Japan's daunting problems — a rapidly aging population, growing national debt and an anemic economy that is the world's third-largest.

The Cabinet that will be announced later Friday will be Kan's third since he took office in June. The one that just resigned was formed in September.

"I will have the most powerful Cabinet," Kan said Thursday at the annual convention of his ruling Democratic Party of Japan held in Chiba, near Tokyo. "The changes will reflect how best we can push for reforms for Japan and tackle the problems."

The reshuffle is largely seen as an attempt to increase chances of passing key legislation, including the 2011 budget. Distracted by personnel issues and a scandal involving a party veteran, Kan's government has been unable to make much progress in parliament.

Kan didn't specify what changes he will make, but Chief Cabinet Secretary Yoshito Sengoku acknowledged he is leaving.

The opposition bloc, criticizing Sengoku for comments he has made on diplomatic and defense issues, threatened to boycott parliamentary sessions if he was not replaced.

Yukio Edano, the ruling party's acting secretary general and Sengoku's close ally, is among the top candidates to be the top government spokesman, swapping positions with Sengoku, according to Japanese media reports.

Kaoru Yosano, a 72-year-old lawmaker who supports raising the sales tax to meet climbing social security costs, said he was tapped as minister of economic and fiscal policy, replacing Banri Kaieda.

Kaieda, an economist and supporter of free-trade zones, is reportedly shifting to economy and trade minister, reflecting the prime minister's push to achieve his goal of opening the country by expanding free-trade deals.

Yosano has held a number of senior posts under the former Liberal Democratic government, and Kan's likely decision to tap him suggests that the prime minister is focused on fiscal reconstruction and wants someone who could foster consensus across party lines.

Finance Minister Yoshihiko Noda, Foreign Minister Seiji Maehara and Defense Minister Toshimi Kitazawa, are among those likely to retain their posts, Kyodo News agency reported.

At Thursday's party meeting, Kan faced criticism from colleagues that his administration was failing to tackle urgent problems confronting Japan.

Tokyo is considering whether to join a U.S.-backed free-trade zone called the Trans-Pacific Partnership, which nine countries are negotiating. Business leaders say Japan must join the TPP or suffer a competitive disadvantage, but farmers are opposed because of worries that cheaper imports would ruin them.