roads, their latest effort to erode sagging voter support for Prime Minister Yasuo Fukuda in a push for a snap election. Parliament's opposition-controlled upper house rejected a law allocating revenue from an unpopular gasoline tax to road construction, although the powerful lower house, dominated by the ruling parties, was expected to override the veto the next day.
Enacting the law, which critics say is an example of ruling party pork-barrel spending, could deepen the slide in Fukuda's support that has stirred talk of him being replaced by a ruling party rival ahead of a general election that must be held by September 2009 but could come sooner.
Recent media surveys have shown support for the 71-year-old Japanese leader has fallen below 20 percent on doubts about his ability to cope with the divided parliament, where the opposition Democratic Party of Japan and smaller allies control the upper house and can delay legislation.
The lower house can override an upper house veto with its two-thirds majority, but the procedure risks a public backlash.
Polls have shown that a hefty majority of voters, unhappy over rising gasoline prices, were opposed to the ruling bloc's use of its two-thirds majority late last month to revive the gasoline tax of 25 yen (24 cents) a liter.
The government has said the gasoline tax was essential to avoid a 2.6 trillion yen gap in national and local revenues.
But the Democrats argue the tax, earmarked for building roads, is a symbol of the long-ruling Liberal Democratic Party's penchant for wasteful spending on vested interests.
Fukuda has promised to shift revenues from the gasoline tax to general spending from the fiscal year starting next April, and the cabinet was expected to pass a resolution to that effect on Tuesday in an effort to address criticism that the 10-year spending law is at odds with his own proposal.
"They have to pass it (the spending bill), because if it doesn't pass, they can't spend the money," said Columbia University professor Gerry Curtis. "Fukuda's popularity will go down even further," he added.
"All he can do is wait for the Diet (parliament) session to end and hope that he can start to turn things around."
The Democrats had threatened to adopt a non binding but embarrassing censure motion against Fukuda over the road related spending, but are now expected to hold back from concern the step and a subsequent halt to parliamentary business might backfire.
"A censure motion is as weighty as a no-confidence motion so we must be circumspect," Azuma Koshiishi, a senior Democratic Party upper house lawmaker told reporters.
"But when it is time to submit one, we will."
Fukuda's inability to break the political logjam has prompted talk of his replacement after less than a year in office.
A poll of 500 voters in the Tokyo metropolitan area published by the conservative Sankei newspaper showed 21.8 percent listed Taro Aso, a right-wing former foreign minister, as their first choice.
