TOKYO (REUTERS) - Mr Shinzo Abe makes no secret of wanting to revise Japan's constitution, which was drafted by the United States after World War Two, to formalise the country's right to have a military - but critics say his plans go deeper and could return Japan to its socially conservative, authoritarian past.

Mr Abe, 58, returned to office in December for a second term as prime minister and is enjoying sky-high support on the back of his "Abenomics" recipe for reviving the economy through hyper-easy monetary policy, big spending and structural reform.

Now he is seeking to lower the hurdle for revising the constitution as a prelude to an historic change to its pacifist Article 9 - which, if strictly read, bans any military.

That would be a symbolic shift, loosening restrictions on the military's overseas activities, but would have limited impact on defence as the clause has already been stretched to allow Tokyo to build up armed forces that are now bigger than Britain's.

However, sweeping changes proposed by Mr Abe's Liberal Democratic Party (LDP) in a draft constitution would strike at the heart of the charter with an assault on basic civil rights that could muzzle the media, undermine gender equality and generally open the door to an authoritarian state, activists and scholars say.

"What I find strange is that although the prime minister is not that old, he is trying to revive the mores of his grandfather's era," said Mr Ryo Motoo, the octogenarian head of the Women's Article 9 Association, a group devoted to protecting the constitution.

"I fear this might lead to a society full of restrictions, one that does not recognise diversity of opinions and puts restraints on the freedom of speech as in the past."

Mr Abe's grandfather Nobusuke Kishi was a pre-World War Two cabinet minister who was arrested but never tried as a war criminal. Mr Kishi served as premier from 1957-60, when he resigned due to a furore over a US-Japan Security Treaty.

Riding high in the opinion polls and buoyed by big stock market gains, Mr Abe has grown more outspoken about his conservative agenda, including revising the constitution and being less apologetic about Japan's wartime past - a stance that has frayed already tense relations with China and South Korea, where memories of Tokyo's past militarism run deep.

Many Japanese conservatives see the constitution, unchanged since its adoption in 1947 during the US-led Allied Occupation, as an embodiment of Western-style, individualistic mores they believe eroded Japan's group-oriented traditions.

Critics see Mr Abe's plan to ease requirements for revising the charter and then seek to change Article 9 as a "stealth" strategy that keeps his deeper aims off the public radar.

"The real concern is that a couple of years later, we move to a redefinition of a 'new Japan' as an authoritarian, nationalist order," said Yale University law professor Bruce Ackerman.

The LDP draft, approved by the party last year, would negate the basic concept of universal human rights, which Japanese conservatives argue is a Western notion ill-suited to Japan's traditional culture and values, constitutional scholars say.

"The current constitution ... provides protection for a long list of fundamental rights - freedom of expression, freedom of religion," said Meiji University professor Lawrence Repeta.

"It's clear the leaders of the LDP and certain other politicians in Japan ... are passionately against a system that protects individual rights to that degree."

The draft deletes a guarantee of basic human rights and prescribes duties, such as submission to an undefined "public interest and public order".

The military would be empowered to maintain that "public order."

One proposal would ban anyone from "improperly" acquiring or using information about individuals - a clause experts say could limit freedom of speech. A reference to respect for the "family" as the basic social unit hints, say critics, at a revival of a patriarchal system that gave women few rights.

"The constitution is there to tie the hands of government, not put duties on the people," said Mr Taro Kono, an LDP lawmaker often at odds with his party on policies.

"There are some in both houses (of parliament) who don't really understand the role of a modern constitution."

Mr Abe and the LDP say easing the revision procedures would allow voters a bigger say in whether to alter the charter.

"The constitution is not something given by God, it was written by human beings. It should not be frightening to change it so I'd like the people to consider trying it once," Mr Yosuke Isozaki, an aide to Abe, told the Nikkei business daily.

An Asahi newspaper survey published on Thursday showed 54 per cent of voters were against easing the procedures compared to 38 per cent in favour. Fifty-two per cent backed revising Article 9 while 39 per cent were opposed.

Under Article 96, changes to the constitution must be approved by at least two-thirds of both houses of parliament and then a majority of voters in a national referendum.

Mr Abe wants to require a simple majority of lawmakers before a public vote.

With Mr Abe's popularity high and the main opposition splintered, the LDP and smaller pro-revision parties appear to have a shot at winning a two-thirds majority in an upper house election in July. They already hold two-thirds of the lower house.

"It's not as easy as it might appear," said Sophia University political science professor Koichi Nakano.

"But for the first time, it's a realistic prospect."

Japan celebrates Constitution Day on Friday.