* Aussie falls as RBA surprises by holding rates
* Dollar and yen rise as Aussie falls after RBA
* Analysts say Aussie may have further room to fall
* Market eyes White House adviser Volcker's testimony
(Adds quotes, updates prices, changes dateline prvs TOKYO)
By Neal Armstrong
LONDON, Feb 2 (Reuters) - The Australian dollar tumbled on Tuesday after Australia's central bank kept interest rates on hold, sparking a sell-off in risk trades and boosting demand for lower-yielding currencies such as the yen and the dollar.
A Reuters poll had shown all 20 economists surveyed expecting the RBA to raise rates by 25 basis points to 4 percent, while markets had been more cautious, factoring in around a 70 percent chance of an increase.
By 0845 GMT, the Australian dollar was testing a five-week low against the U.S. dollar at $0.8782 hit after shedding around 1.4 percent on the announcement.
Against the yen it also shed around 1.4 percent, as carry trades came under pressure.
"The Australian dollar sold off as investors reconsidered their long positions versus the U.S. dollar, the yen and the New Zealand dollar in particular," said Lauren Rosborough, a currency strategist at Westpac.
"There may be more room on the downside, with the December Aussie/dollar low at $0.8735 now a key level to watch."
Risk sentiment will be under scrutiny later when White House adviser Paul Volcker appears before the Senate Banking Committee to defend the administration's proposal to limit risk-trading by banks, which spooked investors and triggered a sell-off in equities when it was unveiled last month.
According to testimony obtained by Reuters, Volcker will urge Congress to curb the risks taken by large banks to help prevent them from being treated as "too big to fail."
"If Volcker says anything specific about possible regulation, equities may react negatively and the dollar and the yen may both strengthen," said Minoru Shioiri, chief manager of FX trading at Mitsubishi UFJ Securities.
The yen had trimmed earlier gains versus the euro to trade down 0.2 percent on the day around 126.01 yen, though the Japanese currency remained in favour against the Australian dollar, trading up roughly 1.4 percent at 79.60 yen.
The dollar was trading flat versus a basket of currencies at 79.20, though still close to its recent six-month highs of 79.534.
The euro recovered from losses to trade unchanged at $1.3920 after initially dropping to $1.3886 on the RBA decision. Investors were eyeing euro zone producer prices data, due for release at 1000 GMT.
Greece's fiscal problems continued to weigh on the euro, analysts said, though the currency showed little reaction to Greek Prime Minister George Papandreou telling a conference the level of Greek bond spreads over euro zone benchmarks was completely unjustified.
Markets were also awaiting a speech by European Central Bank Governing Council member Vitor Constancio, who is also head of the Portuguese central bank.
(Additional reporting by Masayuki Kitano in Tokyo; editing by Nigel Stephenson)