By Charles Scanlon BBC Tokyo correspondent

Japanese Prime Minister Junichiro Koizumi is attempting to burnish his image as a reformer with controversial proposals to deregulate the post office, long a pillar of support for his party.

He intends to introduce four bills to parliament on Friday that could eventually lead to privatisation of the post office.

Powerful members of Mr Koizumi's governing Liberal Democratic Party are deeply opposed to the changes.

Just one year after being swept to office on a wave of public euphoria, Mr Koizumi's political fortunes are at a low ebb.

His approval rating has fallen below 50%, and few now see him as the man to rescue Japan from its political and economic torpor.

His proposals to deregulate the post office are meant to send a signal that he has not given up on reform.

Battle ahead

By appearing to challenge the old guard in his own party, Mr Koizumi will hope to boost his flagging popularity.

The post office is a symbol of the vested interests that are blocking change. Rural postmasters rally support for some of Japan's most conservative politicians.

The postal savings system claims to be the largest bank in the world. Its nearly $2,000bn in deposits are a ready source of funds for pork-barrel projects that help keep the ruling party in power.

Mr Koizumi has long advocated privatisation - to the horror of his rivals. By introducing the bills without full party support, he appears to be spoiling for a final showdown.

But the proposals are relatively limited in scope, hiving off services into a public corporation and allowing only limited competition in postal deliveries.

There will also be plenty of opportunities for compromise once the political haggling gets under way. Mr Koizumi has yet to convince the sceptics that he has the will to bring about fundamental change.