TOKYO – Weakened by scandal and failure at the ballot box, Japan’s prime minister announced yesterday that he was quitting after only a year in office, bowing out amid a political brawl over the country’s aid to U.S. led forces in Afghanistan.

Shinzo Abe surprised members of his party and even his own Cabinet by deciding to resign only days after he pledged to stake his government on the success of legislation to extend Japan’s naval mission in the Indian Ocean.

The nationalist Abe, whose government was severely damaged by a string of scandals and his party’s loss of control of the upper house of parliament in July elections, said someone more politically viable should shepherd the Afghan measure that the opposition is trying to scuttle.

“I decided a quick decision was necessary, and that a further delay would cause political confusion,” he said during a nationally televised news conference. “I find myself unable to keep my promises – I myself have become an obstacle to fulfilling those promises.”

Abe, at 52 the country’s youngest postwar prime minister, listed the election defeat and an opposition leader’s refusal to meet with him earlier in the day as signs that he could no longer lead. Chief Cabinet Secretary Kaoru Yosano said health concerns also contributed to Abe’s decision, but refused to provide details.

It was clear, however, that Abe’s unpopular government had become a liability for the ruling Liberal Democratic Party, which is facing increasing calls from the resurgent opposition to hold early elections for the powerful lower house of parliament.

Four of Abe’s Cabinet ministers have resigned in scandals, including one who quit this month just a week after being appointed. An agriculture minister committed suicide over a money scandal in May.

“It appears Abe finally cracked under the psychological pressure,” said Eiken Itagaki, a political analyst. “He stalled in trying to save his government after the election defeat, and now time has run out.”

A tabloid also has been threatening to publish an article alleging Abe dodged inheritance taxes, Kyodo News agency reported late Tuesday. Abe’s office denied the allegation, the report said.

Abe, whose support ratings in opinion polls had sagged to about 30 percent, did not announce a date for his departure.

The Liberal Democratic Party said it would use a streamlined election process to choose his successor as party president, reportedly on Sept. 19. The party leader is guaranteed election as prime minister because the party controls parliament’s lower house.

Some party lawmakers urged the return of Abe’s charismatic predecessor, Junichiro Koizumi.

“Calls for Koizumi were the loudest,” parliament member Masahiko Shibayama told reporters after a meeting of some ruling party legislators. Kyodo said at least 31 party lawmakers signed a petition calling for Koizumi’s return.

But lawmaker Gaku Ishizaki told TV Asahi that the former premier had so far rejected the idea of returning to power.

Abe’s former foreign minister, Taro Aso, was widely viewed as the front-runner. Aso, a conservative who while serving as foreign minister angered China by calling it a military threat, said it was too soon for him to comment.

The leadership change comes just as the government has opened its battle in parliament over the Indian Ocean naval mission, which the opposition has vowed to defeat.

Japan’s navy has been providing fuel for coalition warships in the Indian Ocean since November 2001 under an anti-terrorism law that has already been extended three times. The legislation is a key issue before the special parliament session that opened Monday.

Although polls show public opinion is split on the issue, the government should eventually be able to push through the legislation because the Liberal Democrats control the lower house, which can override a “no” vote by the upper house.

The United States has turned up the pressure on Japan to extend the mission. U.S. Ambassador Thomas Schieffer met with officials earlier yesterday.