FACTBOX-Possible picks to replace Japan PM Aso

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TOKYO, July 6 (Reuters) - Japanese Prime Minister Taro Aso's sagging support rates and a ruling bloc loss in a closely watched local governor's race are fuelling speculation that his party may seek to replace him before a general election due by October.

Following are some possible candidates to replace Aso as leader of the ruling Liberal Democratic Party (LDP) and premier.

YOICHI MASUZOE, 60

Masuzoe, now health and welfare minister, is a multilingual scholar well-versed in international and domestic politics who often appeared on TV as a commentator before winning an upper house seat in 2001. His mother suffered from dementia in the years leading up to her death, and Masuzoe has written a series of magazine articles about his experiences caring for her.

Though widely seen as competent and hardworking, he has struggled in his current post to reform the national pension system, which has been found to be riddled with errors and fraud.

NOBUTERU ISHIHARA, 52

A reporter turned politician, Ishihara is the son of Tokyo governor Shintaro Ishihara, an outspoken nationalist, but has more moderate views than his father. He was one of five candidates, along with Aso, who ran in September's LDP party leadership race.

An advocate of sweeping reform of the bureaucracy, he has served as transport minister and minister for administrative reform. He was one of several young ruling party lawmakers who worked on steps in 1998 to revitalise Japan's crisis-hit financial sector and is well-versed in economic policy.

SHIGERU ISHIBA, 52

Currently serving as agriculture minister, former defence minister Ishiba is known for what media call a "geeky" knowledge of security issues and has written several books on defence.

Ishiba gained a reputation as an unflappable debater when the LDP wrestled with the powerful opposition over the renewal of a legal mandate for marine refuelling in the Indian Ocean in support of U.S.-led military operations in Afghanistan.

He stood against Aso in a party leadership race in September.

YURIKO KOIKE, 56

A former TV announcer fluent in English and Arabic, Koike served briefly as Japan's first woman defence minister in 2007.

She ran in the ruling party leadership race last year in a bid to become the country's first female prime minister on a platform pledging to stick to popular former premier Junichiro Koizumi's market-oriented reforms.