TOKYO (Reuters) - Japanese Prime Minister Shinzo Abe drafted the popular son of ex-premier Junichiro Koizumi in a broad reshuffle on Wednesday that also packed his cabinet with conservative allies, as he faces a tax rise and aims to amend the pacifist constitution.

Japan's Prime Minister Shinzo Abe leads his cabinet ministers as they prepare for a photo session at Abe's official residence in Tokyo, Japan, September 11, 2019. REUTERS/Issei Kato

Abe told a news conference after the new line-up was launched that constitutional reform, a long-held goal of his ruling Liberal Democratic Party (LDP), was among the difficult challenges his cabinet faced that he was “resolved to accomplish by all means”.

Abe chose telegenic Shinjiro Koizumi, who regularly tops lists of lawmakers whom voters favor to succeed to the nation’s top job, as environment minister.

Koizumi was one of 13 first-time ministers among 19 whose appointments were announced on Wednesday. At 38 years of age, Koizumi becomes the third-youngest to win a portfolio in post-war Japan, media said

His appointment, although to one of the less powerful cabinet posts, could give a popularity boost to the new line-up.

It could also bolster Koizumi’s chance of competing to succeed Abe when the prime minister’s term as ruling LDP chief ends in September 2021.

Abe, who returned to power in December 2012 promising to reboot the economy and bolster defense, is already on track to become Japan’s longest-serving premier in November.

Koizumi - popularly known as Shinjiro to distinguish him from his father - grabbed headlines last month with news that he would marry Christel Takigawa, a French-Japanese television presenter, and they would soon have a baby.

His charismatic father led Japan from 2001 to 2006.

Abe, although drafting more than a dozen new faces, retained his close allies, Finance Minister Taro Aso, 78, and Chief Cabinet Secretary Yoshihide Suga, 70. Both have served in their posts since Abe - whose first, year-long stint as prime minister immediately followed the elder Koizumi - returned to office.

Many others are also allies sharing Abe’s conservative agenda, including revising the post-war constitution.

“It looks like the ultimate buddy-buddy cabinet,” said Norihiro Fujito, chief investment strategist at Mitsubishi UFJ Morgan Stanley.

Aso must help ensure the economy weathers an increase in the sales tax to 10% from 8% in October, which could dampen consumption when a U.S.-China trade war is clouding growth.

POSSIBLE HEIRS

Abe kept veteran lawmaker Toshihiro Nikai, 80, as LDP secretary general and Fumio Kishida - also considered a possible heir to the premier - as party policy chief.

Several ministers are also seen as possible contenders to succeed Abe, including Suga.

Another would-be premier is Toshimitsu Motegi, 63, a Harvard-educated lawmaker with a reputation as a tough negotiator who replaced Taro Kono as foreign minister.

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Motegi, who as economy minister handled tough trade talks with the United States, will keep that portfolio, Abe said.

Kono, 56, another potential future premier, was appointed defense minister, media said.

A fluent English speaker well-known in Washington, Kono has a reputation as a maverick. He has been on the front line of Japan’s feud with South Korea over wartime history and trade.

Another Abe ally and potential future premier, former health, labor and welfare minister Katsunobu Kato, returned to his old post.

Abe appointed a former Olympic speed skater, Seiko Hashimoto, as Olympics minister to prepare for the 2020 Games in Tokyo, one of two women to win posts.

Abe, who could seek a rare fourth term as LDP leader in 2021 if party rules change, has made clear he intends to pursue his goal of revising the post-war, U.S.-drafted constitution to clarify the status of the military.

The charter, if taken literally, bans a standing military, but has been stretched to allow armed forces for self-defense.

Abe’s task got tougher when his LDP-led coalition lost its two-thirds majority in a July upper house election. Amendments to the charter require approval by two-thirds of each chamber of parliament and a majority in a referendum.

“Revising the constitution is difficult and if once it is rejected in a referendum, it could become impossible to debate,” said Hiroyoshi Sunakawa, a professor at Rikkyo University, adding Abe could try to combine the plebiscite with a snap general election at some point next year.