TOKYO (AFP) - Japan wants its athletes to double their best-ever medal haul at the 2020 Tokyo Olympics, but experts warn the debt-laden nation will need to spend big if it is to seize the homefield advantage.

Hosting the Games traditionally brings a bump in the medals table - Britain bagged 29 golds in London last year against 19 in 2008 in Beijing, while Japan's best figure of 16 gold medals came in 1964 at the first Tokyo Olympics.

Japan's education ministry, which is charged with overseeing sport, wants its 2020 team to get 70 to 80 medals, of which 25 to 30 should be golds.

That would put the country between third and fifth in the medals table - based on results from recent Games - a position sought by the Japanese Olympic Committee (JOC) under its medium-term plan and seen as an appropriate placing for the world's number-three economy.

"It will be very difficult," sports sociologist Toshio Saeki said, adding China and South Korea will also ramp up their efforts to remain Asia's number-one and number-two sporting powers ahead of Japan.

"But setting a high goal like this could help as it will urge people to work hard," said Mr Saeki, a professor at the Japan Sports Wellness University.

But, say experts, already heavily indebted Japan needs to invest a lot of money in developing Olympic wannabes if it is to get anywhere near its goal in seven years' time.

"Japan will put its efforts into athlete training, although I cannot tell if it will be in a sufficient way," said Tsukuba University assistant professor Yoshio Takahashi, a sports management expert.

"Japan is a country whose sports-related budget has been limited by world standards."

The country already has a debt-to-GDP ratio of more than 200 per cent, and tax revenues are shrinking as its society ages and fewer young workers contribute to state coffers.

But sports experts say proper investment is key if Japan is to realise its dreams, pointing to the dividends it has paid for previous Olympic hosts.

At London 2012, Britain's 29 golds propelled it to third in the table, a robust recovery from the 1996 Atlanta Games where it picked up just one.

Britain spent 264 million pounds (S$529 million) over four years to train Olympic athletes, with much of the money coming from a national lottery.

For Vancouver 2010, Canada spent 117 million Canadian dollars (S$140 million) on Winter Olympic training and lifted a table-topping 14 gold medals.

Tokyo's education ministry has asked for its biggest ever settlement, requesting 49 billion yen (S$618 million) in its sports-related budget for the 2014-2015 fiscal year.

But nearly half of the sum would be used in the first phase of a project to build a new 80,000-seat National Stadium, the centrepiece of the 2020 Games.

So far, there is no extra money being planned for sport, although Prime Minister Shinzo Abe has offered assurances that it will be forthcoming, despite the crimp on budgets brought about by the shrinking workforce and ballooning cost of social care.

In August, the government pledged to cut a whopping US$82 billion (S$101 billion) out of its budget over two years as it works to bring down the industrialised world's biggest debt mountain.

Training expenditure has been and will be focused on sports in which Japan usually wins medals, such as swimming, women's football, men's gymnastics, wrestling and judo.

Some extra cash has come from a public body established in 2003 to promote sport and to run a football results lottery.

Part of the plan is the creation of an "agency of sport" that can help guide investment towards developing elite athletes, now focused on promising youngsters aged between 16 and 20 who could be expected to reach their competitive peak for the Tokyo Games.

"We are seeking to step up in areas where we narrowly missed gold," said JOC athlete development official Naoya Yanagiya, after what many saw as a disappointing haul in London, where despite a record 38 podium finishes, just seven were gold.

The planned launch of the agency for coordinating sports-related government policies and actions will "make it easy for us to secure a budget for athlete development and help improve our competitive skills", said Ms Seiko Hashimoto, a senator and JOC senior executive in charge of athlete development.

But the seven-time Olympian, who took part in both Winter and Summer Games, taking home the 1,500-metre speedskate bronze in 1992 and producing modest results in cycling, admitted it was a big ask.

She said when it sank in that Tokyo's bid had been successful she had a "choking feeling under the weight of responsibility".

But "if we take advantage of competing at home, it won't be a dream for us to get the biggest-ever number of medals".