TOKYO (Reuters) - - Japan could hold its first referendum on revising its pacifist constitution next year, a historic step which if successful would cement Prime Minister Shinzo Abe’s conservative legacy but risks splitting the public and worrying China and South Korea.

Japan's Prime Minister Shinzo Abe speaks on reports of the launch of a North Korean missile to reporters , at his official residence in Tokyo, Japan May 29, 2017. REUTERS/Toru Hanai

Abe, in a surprise move on the 70th anniversary of the U.S.-drafted charter last month, made a proposal to revise its war-renouncing Article 9 by 2020 to clarify the ambiguous status of its military, known as the Self-Defense Forces (SDF).

Amending Article 9 would be hugely symbolic for Japan, where supporters see it as the foundation of post-war democracy but many conservatives see it as a humiliating imposition by the U.S. Occupation after Japan’s defeat in 1945.

It would also be a victory for Abe, whose conservative agenda of restoring traditional values and loosening constraints on the military centres on revising the constitution.

“When he looks back on his years in office, he wants to be able to say, ‘I revised the constitution’,” said former deputy defense minister Akihisa Nagashima.

Concrete steps to change the charter would likely cause concern in China and South Korea, where bitter memories of Japan’s past military aggression persist, although analysts said Seoul’s new government might refrain from direct criticism given the need for cooperation over North Korea’s missile programmes.

“Because of reasons of history, the international community, particularly Asian neighbors, have always paid close attention and been on alert to Japan’s military tendencies,” Chinese Foreign Ministry spokeswoman Hua Chunying said recently.

China hoped Japan could “respect the spirit of the peaceful constitution”, she said.

Abe’s proposal would add a clause legitimizing the SDF to existing clauses renouncing Japan’s right to wage war and banning the maintenance of armed forces.

While similar to a past proposal from his Liberal Democratic Party’s dovish junior partner, the proposal is a step back from more drastic changes sought by his LDP.

“Abe lowered the hurdle considerably,” said Hajime Funada, deputy head of an LDP task force on constitutional reform, told Reuters.

The LDP could draft a proposal by year-end and parliament could vote next year, followed by a referendum, he said.

Past Japanese governments have interpreted Article 9 to allow the existence of a military for self-defense.

In a contentious shift in 2015, parliament enacted laws allowing Japan to exercise collective self-defense, or aiding allies under attack, but based on a reinterpretation of the constitution rather than a formal revision.

The impact of any change on Japan’s defense policies is a matter of heated argument.

Proponents of the change say Abe’s proposal would simply inscribe in the constitution existing policies but critics worry it would open the door to an expansion of the SDF’s role abroad.

Formal revision requires approval of two-thirds of both houses of parliament and a majority of voters in a referendum.

CLOCK TICKING

Proponents of change say it is time for a formal amendment.

“What we must do is properly authorize the SDF, not through an invisible interpretation, but in a form that is clear,” Masahiko Shibayama, an adviser to Abe, told Reuters.

The clock, however, is ticking.

Even if Abe wins a third three-year term as LDP leader and hence, premier, when his tenure ends in 2018, the ruling bloc and its allies could well lose their two-thirds majority in a lower house election that must be held by late that year.

Japanese voters are divided.

Support for revising Article 9 has actually dropped from 30 percent in 2002 to 25 percent early this year, according to surveys by NHK public TV, a decline some experts attribute to mistrust of Abe’s conservative ideological agenda.

But in a late May poll by the Nikkei newspaper, 51 percent backed Abe’s proposal, an apparent sign many could accept a change they think would merely legitimize the status quo.

Opponents of revision, who think Abe’s government has already stretched the constitution too far with the collective self-defense legislation, however, suspect it would use the proposed amendment to widen further the military’s role abroad.

“In spite of Article 9, the SDF has grown to be as large as the British military,” said Sophia University professor Koichi Nakano.

“It is clear that the motive behind the revision of the constitution has always been to undo the post-war pacifist constraints, and that is exactly what they are seeking to accomplish,” he said.