* Dollar/yen slips to Y83.25 ahead of Japan party vote
* Dlr index near 1-mth low, clings to 200-day moving average
* Pound drops on surprise weakness in British house prices
* Kiwi down on weak NZ retail sales, near 4-mth low vs Aussie
By Hideyuki Sano
TOKYO, Sept 14 (Reuters) - The dollar slid to a new 15-year low against the yen on Tuesday ahead of a Japanese ruling party leadership vote in which the prime minister faces a challenge from a proponent of more aggressive fiscal stimulus.
The dollar was also near a one-month low against a basket of currencies after suffering its steepest fall against the euro in two months the previous day as rising investor risk appetite helped the European currency.
Japanese media surveys have shown the race between Prime Minister Naoto Kan and party heavyweight Ichiro Ozawa is too close to call ahead of a party conference due to start at 0500 GMT. The result is expected at around 0630 GMT.
"If Kan wins, the market will try to sell the dollar, betting that Japan cannot intervene and sell the yen at this stage," said Daisuke Karakama, a market economist at Mizuno Corporate Bank.
As Ozawa has been more emphatic than Kan in saying he would consider currency intervention, even solo intervention, some market players would see an Ozawa victory as positive for the dollar, at least in the near term.
But any rise in the dollar may be short-lived given expectations of more dollar selling from Japanese exporters ahead of their half-year book closing on Sept. 30.
"There are some expectations of an Ozawa victory. But many traders are not looking to buy more dollars. They just want to sell the dollar if there was intervention that would push up the dollar," said a trader at a Japanese bank.
Junya Tanase, a currency strategist at J.P. Morgan Chase Bank, said the dollar could fall even if Ozawa wins as Ozawa's reflationist policy platform could boost Japanese bond yields, shrinking the yield gap between Japan and the United States.
"We think there is little difference between the two candidates in their stance on intervention. But an Ozawa victory could boost Japanese bond yields as the bond market seems to be sensitive about fiscal deterioration," Tanase said,
Japanese bond yields started to spike on Aug. 26, the day Ozawa announced his bid for the party leadership.
The dollar fell to 83.25 yen, before settling at around 83.40 yen, down about 0.4 percent on the day.
The dollar/yen rate has closely tracked U.S.-Japan yield gaps, partly because a smaller gap means less incentive for Japanese investors to buy U.S. debt instruments. And on Monday, dollar/yen came under pressure due to falls in U.S. bond yields despite strength in global shares.
The euro traded at $1.2870, down slightly on the day but keeping much of Monday's 1.6 percent gains following solid data from China and relief over new Basel III banking rules.
It faces a major resistance point around around $1.2920-30, a level that has blocked the currency a few times since August.
The dollar index is languishing at 81.86, down slightly on the day and near a one-month low of 81.760 hit on Monday and its 200-day moving average of 81.761.
Although the index recovered from a brief foray below the 200-day moving average last month, another break below that could stoke pessimism over the U.S. currency.
The British pound fell 0.1 percent to $1.5400 after surprisingly weak house price data.
The New Zealand dollar dropped about 0.6 percent to $0.7295 after weaker-than-expected New Zealand retail sales added to the case against a rate hike.
That rate outlook contrasts sharply with Australia, where strong job data has raised expectations of a future rate hike, lifting the Aussie against the New Zealand dollar.
The Australian dollar rose about 0.4 percent to NZ$1.2790, edging closer to a four-month high around NZ$1.2845 hit earlier in the month.
Against the U.S. dollar, the Aussie dollar fell 0.1 percent to $0.9334, still a whisker from five-month high around $0.9363 struck on Monday. (Editing by Edwina Gibbs)