Prime Minister Yasuo Fukuda's support rates have already slid below 20 per cent in some polls, prompting talk that his ruling party will seek to replace him ahead of a general election that must be held by Sept 2009 but could come sooner.

A mere 13 per cent of voters approved the use of the ruling camp's two-thirds lower house majority to override an upper house veto of the bill, which allocates funds from a controversial gasoline tax for road construction, according to a survey by NHK public television published the previous day.

Support for the main opposition Democratic Party of Japan (DPJ), keen to force an early lower house election, rose nearly 10 points to 27.1 per cent in the poll, while backing for Mr Fukuda's Liberal Democratic Party (LDP) fell almost five points to 25.6 per cent.

The Democrats say the law is an example of LDP pork-barrel policies and contradicts Mr Fukuda's own proposal to shift revenues from a controversial 25 yen (S$0.32) per litre gasoline tax, now earmarked for roads, to general spending from 2009/10.

Opposition unimpressed
To address such criticism, the cabinet earlier on Tuesday adopted a resolution pledging to carry out Mr Fukuda's proposal, but the opposition was unimpressed.

'What sort of act is it to try to enact forcefully ... a law that continues the wasteful spending of the past, despite its rejection by the upper house?' Democratic Party executive Naoto Kan asked the lower house of parliament. 'For the lower house to vote again on this bill ... without even revising it is just nonsense.'

It was the third time Mr Fukuda's government used the ruling bloc's two-thirds majority, won in 2005 under charismatic leader Junichiro Koizumi, to override a veto by the upper house, where the DPJ and smaller allies won a majority last July.

The Democrats had threatened to adopt a non-binding but embarrassing censure motion against Mr Fukuda over the road-related spending, but are now expected to hold back.

Instead, they hope to impress voters by grilling Mr Fukuda in parliament on such matters as a new, unpopular scheme for elderly health insurance that raises the burden for some people aged 75 and over, a demographic that already accounts for one-tenth of Japan's fast-ageing population.

With the ratings of both Mr Fukuda and his party falling, political analysts say the prime minister will be wary of calling a general election any time soon.

But speculation persists that he or his successor may go to the polls in the autumn after Japan hosts a Group of Eight leaders' summit in July. -- REUTERS