Japan's Prime Minister Naoto Kan, in office for just three months, fights for his job on Tuesday in a party vote against a veteran powerbroker who could become the nation's third leader in a year.
Ichiro Ozawa, although less popular with the public and tainted by money scandals, is seen as having an even chance in the internal party ballot because he commands the loyalty of many lawmakers he helped get elected.
For Japan and its young centre-left government, the power struggle spells more instability at a time when its stuttering economy has been overtaken by China and ties are lukewarm with Washington and tense with Beijing.
Even if Kan survives the political showdown, observers fear the rift it has created within his Democratic Party of Japan (DPJ) will damage the party that one year ago ended a half-century conservative reign in a landslide.
Ozawa, 68, a veteran backroom operator, was credited with being the architect of last year's stunning victory who hand-picked and coached an army of first-time politicians, sometimes dubbed "Ozawa's children".
Their loyalty is seen as his strength in the ballot where the voting power of 411 DPJ lawmakers far outweighs that of the total of 340,000 rank-and-file party members, who already cast their secret ballots by mail last week.
At a party meeting starting at 2:00 pm (0500 GMT) at a Tokyo hotel, the two candidates for the party presidency are due to speak for 15 minutes each before the vote, with a result expected in the afternoon.
The winner is virtually assured of taking the premiership because the DPJ holds a majority in the powerful lower house of parliament, even though it received an electoral drubbing in the upper house in July.
Ozawa, sometimes dubbed the "Shadow Shogun", was seen by many as the fixer behind the first DPJ premier, Yukio Hatoyama, who came to power a year ago but resigned in June amid rock-bottom poll ratings.
When Hatoyama stepped down, he apologised for mishandling a row over a US airbase on Okinawa island and for political funding scandals that have also dogged Ozawa, who resigned with him as party secretary general.
Upon taking office in June, 63-year-old Kan, a social activist in the 1970s, distanced himself from Ozawa, and has repeatedly promised "clean politics".
If Ozawa, who announced his bid only three weeks ago, wins, he would become Japan's sixth premier in four years, continuing a "revolving-door" leadership system often blamed for reducing Tokyo's influence on the world stage.
As the rivals have debated, worries about the economy have dominated as fast-greying Japan remains stuck in two decades of slow growth, stagnant demand and falling prices with its export sector battered by a strong yen.
Ozawa has advocated higher stimulus spending and market intervention to bring down the yen, while Kan has stressed the need for fiscal austerity to reduce a huge debt mountain and has pledged to focus on creating jobs.
On foreign policy, Ozawa, who weeks ago called Americans "simple-minded", has said he may seek to renegotiate a row over a US base, an issue which has angered Okinawans and soured ties with the Obama administration.
Ozawa has also long cultivated closer ties with China, Japan's traditional Asian rival, which has bitterly protested in recent days over Japan's arrest of a Chinese fishing boat captain near a disputed island chain.
AFP/de
