By Linda Sieg

TOKYO (Reuters) - Japanese Prime Minister Shinzo Abe was widely expected to appoint conservative ally Tomomi Inada as defense minister on Wednesday, a move that could upset China and South Korea, while keeping key ministers in their posts in a cabinet rejig.

Inada, the ruling party policy chief, shares Abe's goal of revising the post-war, pacifist constitution, which some conservatives consider a humiliating symbol of Japan's World War Two defeat.

The 57-year-old lawyer regularly visits Tokyo's Yasukuni Shrine for war dead, which is seen as a symbol of Japan's past militarism in China and South Korea.

Japan's relations with Beijing and Seoul have often been frayed by the legacy of Japan's military aggression before and during World War Two.

"Ms. Inada is an ultra-conservative politician and this will be taken as preparation for achieving constitutional revision and adopting a stern stance toward China," said Takashi Kawakami, a security expert at Takushoku University.

Inada would be the second woman to hold the defense post.

Abe is trying to rekindle economic growth and cope with several diplomatic challenges as he ponders the possibility of staying in office after his term as president of the ruling Liberal Democratic Party (LDP) ends in 2018.

He is expected to travel to China in September for a Group of 20 summit, and may meet Chinese President Xi Jinping there.

Sino-Japanese ties have also been strained by a row over tiny isles in the East China Sea and China's growing assertiveness in the South China Sea.

Abe, who took office in December 2012, will retain his right-hand man, Chief Cabinet Secretary Yoshihide Suga, along with Finance Minister Taro Aso and Foreign Minister Fumio Kishida, media reported.

Economics Minister Nobuteru Ishihara may be kept on along with Health, Welfare and Labour Minister Yasuhisa Shiozaki. Public broadcaster NHK has said Deputy Chief Cabinet Secretary Hiroshige Seko would become trade and industry minister.

Shigeru Ishiba, minister for regional revitalization, was expected to leave the cabinet, media reported, to prepare for a run at replacing Abe as prime minister when his term as LDP leader expires.

Abe will also appoint a new LDP executive line-up on Wednesday. The expected appointment of Toshihiro Nikai, 77, a big-spending advocate with good ties with China, as LDP secretary general was seen as signaling Abe's hopes for a third term. Nikai has said he would support an extension for Abe, which would require a change in party rules.

On Tuesday, Abe's outgoing cabinet approved 13.5 trillion yen ($133.58 billion) in fiscal steps to try to revive the economy.

Some analysts worry Abe will devote too much energy to trying to revise the constitution after his ruling bloc and allies obtained the two-thirds majorities in both houses of parliament needed to begin the process. Changes must also be approved in a referendum.

($1 = 101.0600 yen)