TOKYO » A former top diplomat vying to become the next prime minister proposed Saturday that Japan stop building new nuclear power plants after the Fukushima disaster and phase out atomic energy over 40 years.

Former Foreign Minister Seiji Maehara took the clearest stand against nuclear power at a news conference where five ruling Democratic party members outlined their policy goals in their campaign to replace Prime Minister Naoto Kan, who announced Friday he is stepping down.

The ruling party will vote Monday to pick a new party chief, who will then become prime minister — Japan’s sixth in five years.

Nuclear energy is hot topic in Japan following the accident at the Fukushima Dai-ichi nuclear power plant, damaged by the March 11 tsunami. Some 100,000 people have been evacuated from around the plant, and government officials have warned that accumulated radiation in some spots may keep areas off limits for the foreseeable future.

The leadership contest is emerging as a close race between Maehara, a youthful defense expert and the public’s top choice, and Economy Minister Banri Kaieda, who secured the backing of the ruling party’s behind-the-scenes powerbroker, Ichiro Ozawa.

"In principle, we will not build new nuclear plants; then there will be no more nuclear plants in 40 years," Maehara said, adding that Japan needs to seek "the best energy mix" while it phases out of its nuclear-reliant energy policy.

Before the March accident, Japan derived about 30 percent of its electricity from nuclear plants, and the government intended to increase that to 50 percent by 2030 — a plan that has now been scrapped.

Kaieda, whose minister was broadly responsible for nuclear energy promotion, said he planned to decommission aging nuclear plants found to have problems during stress tests, but did not detail his vision for the future of atomic energy.

He promised to speed up decontaminaton efforts and launch health check programs for concerned residents.

"We will achieve a cold shutdown of the reactors as soon as possible," Kaieda said. "I will take concrete measures to address the residents’ concerns about their health."

Kan announced Friday he would resign after serving nearly 15 months that have been plagued by ruling party infighting, gridlock in parliament and clamorous criticism of his administration’s reponse to the March disasters and ensuing nuclear crisis.

The Japanese public, yearning for political unity and resolve in the wake of the catastrophe, has grown disgusted with the squabbles and blame-trading that have dominated parliamentary sessions.

"It’s embarrassing. It’s hard to keep track of who’s prime minister these days," said Rie Aoki, a housewife in the Tokyo suburb of Fuchu. "It’s so upsetting to see them squabbling in parliament. Elementary students have more interesting conversations."

She said she hoped the politicians would focus on the northeastern coastal region — called Tohoku — that was devastated by the tsunami. "I really want them to work together to think about what Tohoku needs," she said.

The five candidates generally agreed during the two-hour press conference that the central government needed to spend more money on disaster reconstruction in the tsunami zone, possibly raising money through special bond sales.

Given the slow economy, all agreed it was too early to consider raising Japan’s 5 percent sales tax.

But the gathering also helped bring out some policy differences between the five, which also includes Finance Minister Yoshihiko Noda, considered a fiscal conservative, former Transport Minister Sumio Mabuchi and Agricultural Minister Michihiko Kano.

Maehara said he would favor reaching out to key opposition parties to form a limited "grand coalition" on certain key policies, such as tsunami reconstruction, social security and tax reforms. Maehara also said he would support a U.S.-backed free trade zone called the Trans-Pacific Partnership.

Kaieda, a 62-year-old former television commentator on economic matters, said the so-called TPP needed to be studied more and rejected the idea of a grand coalition, saying the party had not even discussed such a proposal.

A China hawk, Maehara, 49, gained prominence by taking a firm stand toward Beijing during a territorial spat last year over some disputed islands in the East China Sea.

He defended his decision to run despite having quit as foreign minister in March after it was discovered that he had unknowingly received a relatively small political donation from a foreigner — a Korean permanent resident and a childhood friend — which is illegal in Japan.

"I don’t have anything to hide," he said. "I haven’t done anything that tainted my own hands."

Associated Press writer Mari Yamaguchi contributed to this report.