By Linda Sieg
TOKYO (Reuters) - When Prime Minister Shinzo Abe holds a ceremony on Sunday to mark a day in history that few voters give much thought, he will also be quietly pushing his agenda to break free from Japan's post-war pacifism that could risk inflaming regional tensions.
This week's friction with China and South Korea over disputed territory and history showed once more that the past still looms large over diplomacy in East Asia.
The conservative Abe's efforts to recast that history in a less apologetic tone and ease the limits of a pacifist, U.S.-drafted constitution on the military are likely to further strain already fraught ties with Beijing and Seoul.
The popular 58-year-old Abe, who regained office for a rare second term in December, had pledged in his Liberal Democratic Party's campaign platform to make April 28 "Return to Sovereignty Day", marking the formal end of U.S.-led Allied occupation seven years after Japan's defeat in World War Two.
Seoul and Beijing may have little to say about a commemoration of the day the San Francisco Treaty took effect, but the ceremony has a less overt but equally vital message.
"Abe is laying the groundwork for revising the constitution. He wants to remind people that the war is over, the post-war period is over, we are in the 21st century and it is time to turn the page," said Jeffrey Kingston, director of Asian studies at Temple University's Japan campus.
"But it's not so easy. Japan doesn't get to make the call because its neighbours are eager to keep Japan twisting on the hook of history."
Abe is enjoying sky-high popularity ratings of over 70 percent as voters applaud his "Abenomics" prescription for boosting the long-stagnant economy with a mix of hyper-easy monetary policy, big spending and structural reform.
Some of Abe's advisers want him to focus on the economy while keeping his conservative agenda on the backburner, at least until after a July upper house election that the ruling bloc needs to win to cement his grip on power.
But those same high voter ratings appear to be encouraging Abe to show more of his ideological colours, signing off on a visit by his deputy to Tokyo's Yasukuni Shrine for war dead, seen by critics as a symbol of past militarism, and warning Japan was prepared to "use force" to defend Japanese-controlled islands in the East China Sea that China also claims.
"It is only natural to honour the spirits of the war dead who gave their lives for the country. Our ministers will not cave in to any threats," Abe told a parliamentary panel on Wednesday. "It is also my job to protect our pride, which rests on history and tradition."
A further flare-up in disputes, with Beijing especially, could threaten the success of "Abenomics" if it damages business ties, which were hit hard last year after a decision by the Japanese government to nationalise disputed isles in the East China Sea triggered violent anti-Japanese protests in China.
"Think how many business executives working in China are tearing their hair out, thinking 'not again'," Kingston said. "China is absolutely crucial to Japan's economy."
Historic bitterness over Japan's wartime aggression resurfaced this week after Abe sent a ritual offering and his Deputy Prime Minister Taro Aso visited Yasukuni Shrine. More than 160 lawmakers also paid their respects on Tuesday at its annual spring festival.
Leading politicians' visits to the shrine, where 14 Japanese leaders convicted as war criminals by an Allied tribunal are honoured with the country's war dead, have long angered Asian countries where memories of Japan's past militarism run deep.
Tensions also heated up in a Sino-Japanese row over the disputed islands, known as the Senkaku in Japan and the Diaoyu in China, after a flotilla of Japanese nationalists sailed near the rocky islets and China sent eight surveillance ships into what Tokyo considers its waters.
Abe has spoken out with greater frequency in recent weeks about his desire to revise the constitution, first by lowering the bar for future changes. Under the charter's Article 96, revisions must be approved by two-thirds of both houses of parliament before holding a national referendum, where a majority must back the change. Abe wants to require a simple majority of lawmakers ahead of the national public vote.
Sunday's ceremony "is certainly a prelude to revising the constitution. The logic is the same: that we lost our sovereignty, we regained it after the occupation but it will not be fully regained until we revise the constitution that was imposed on us," said Sophia University professor Koichi Nakano.
"It is giving a foretaste of what is to come."
(Editing by Alex Richardson)