* Tumble in Wall Street, domestic political woes hurt market
* Political vacuum seen regardless of PM no-confidence motion outcome
* Foreign investor buying slows
* Nikkei support seen around 9,400
By Hideyuki Sano
TOKYO, June 2 (Reuters) - Japanese share prices fell sharply on Thursday, dragged lower by a steep fall in Wall Street after disappointing data and by growing political uncertainty as Japanese Prime Minister Naoto Kan faces a no-confidence motion later in the day.
Kan was at risk of losing his job after rebels in his own party said they would back the no-confidence motion, threatening political chaos as the government struggles to contain a nuclear crisis and rein in massive public debt. [ID:nL3E7H200W]
"Whatever the outcome, a political vacuum is unavoidable," said Daisuke Uno, chief strategist at Sumitomo Mitsui Banking Corp.
"As the global equity rally based on economic optimism since last November is running out of steam, Japanese shares are suffering from problems both at home and abroad, and their prices will be coming under pressure," he added.
The Nikkei share average fell 1.6 percent to 9,568.87, giving up a large portion of the gains accumulated over the past two sessions.
The broader Topix dropped 1.7 percent to 825.48.
The fall was slightly smaller than the 2.2 percent decline in the Dow Jones industrial average on Wednesday, which analysts say is natural given that Japanese shares underperformed during the rally in the U.S. and in other developed countries' stocks in recent months.
Wall Street shares made a dismal start to June, typically a weak month for the market, after both private payroll data and a key manufacturing survey missed estimates.
In the Nikkei, support is seen around 9,400, a low hit in late April and May. Many market players say there are few reasons to sell sharply below that level as Japanese shares are already trading at around book value.
"U.S. shares needed a correction of their recent steep gains. Japanese shares will be capped for now but cheap valuations will give the market support," said Ryota Sakagami, a strategist at Nomura Securities.
But market players also said buying by foreign investors -- a major driving force behind the Nikkei's rebound from a two-year low right after the earthquake and nuclear accidents in March -- appears to be waning.
Data from Japan's Ministry of Finance showed on Thursday that foreign investors sold a net 83.2 billion yen of Japanese shares last week, their first net selling in nine weeks in the data series.
And Japan's chaotic politics could further dampen appetite.
"Foreign investors have been buying not just exporter shares but also domestic demand-sensitive shares such as consumer cyclicals," said Nomura's Sakagami.
"For these shares, domestic policy is an important factor. Political uncertainty will make foreign investors hold off from buying Japanese stocks."
A lower house session to vote on the no-confidence motion was to open at 1 p.m. (0400 GMT), with the vote expected around 3 p.m. (0600 GMT) after speeches for and against the motion.
Even if Kan -- already Japan's fifth premier in as many years -- survives, the ruling party split will further handicap efforts to implement policies in a divided parliament, including politically sensitive tax reforms.
If the motion passes, Kan will have to either step down or call an election.
While some say the removal of Kan could open the way for a more politically stable government such as grand coalition between the ruling Democrats and opposition parties, others note that political stalemate is likely to continue.
"While there are many possible scenarios for political realignment, that will lead to political chaos and cap share prices," said Hideyuki Suzuki, general manager of market research at SBI Securities.
"Some say this could lead to hopes for stronger leadership after political reorganisation but I think that is unlikely as there is no clear successor even among opposition parties." (Additional reporting by Daiki Iga; Editing by Joseph Radford)