* Market optimism gives way to caution, lifting yen, dollar
* BOJ keeps rates steady, expands assets used for market ops
* RBA cuts rates by 25 bps to 3.0%, Aussie pulls off lows
By Kaori Kaneko TOKYO, April 7 (Reuters) - The yen and the dollar rose on Tuesday as renewed nervousness about banks' health stalled a rally in riskier assets, but the Australian dollar climbed after its central bank opted for a modest rate cut.
With many Asian stock markets in the red after a fall on Wall Street on Monday, the yen and the dollar benefited as investors took defensive positions and pocketed profits from a recent run higher in the euro and higher yielding currencies.
But the Australian dollar rose against the greenback after the Reserve Bank of Australia, in a much-awaited decision, cut its key cash rate by 25 basis points to a record low of 3.0 percent, less than some had wagered.
The Aussie hit a three-month high against the dollar last week and a five-month peak against the yen on Monday as a rise in risk tolerance made it and other higher yielding currencies a target for short-term yield plays.
It then fell early on Tuesday as a warning about banks knocked stocks down and boosted demand for dollars and yen.
"With the uptrend of the Aussie, market players were looking for chances to buy on the dips. So after the uncertainty factor got cleared away, they were comfortable buying back the currency," said Mitsuru Sahara, chief manager at Bank of Tokyo-Mitsubishi UFJ.
"There is demand for the Aussie from those who want to bet on the economic recovery," he said.
The Aussie rose 0.2 percent on the day to $0.7133 and pulled off the steepest of its lows against the yen to stand just 0.4 percent down at 71.70 yen. It leapt to a six-month high of 72.87 yen on Monday.
AFTER THE RALLY, THE PROFIT-TAKING
The Bank of Japan kept rates steady at 0.1 percent as expected and unveiled further steps to ease credit strains, as the world's No.2 economy wallows in its worst postwar recession amid a global credit crisis.
The central bank also expanded the range of collateral eligible for market operations to include loans on deeds to the government, loans with government guarantees and loans on deeds to municipal governments.
The dollar eased once the decision was out of the way, falling 0.6 percent on the day to 100.41 per dollar.
It had hit its highest in nearly six months on Monday, at 101.45 yen, and one analyst said it needed to remain above 99.70 yen, which was the breakout point for its latest leg higher, if it were to stave off a deeper correction.
The euro fell 0.8 percent to 134.50 yen, after touching 137.42 yen on Monday, its highest since late October.
It fell 0.3 percent on the day to $1.3375, while the dollar also gained against sterling and the New Zealand dollar.
Traders said the decline in the euro and higher yielding currencies was driven by profit-taking after their recent gains, as well as jitters about the health of the banking sector.
UK daily the Times said on its website that new IMF forecasts were set to suggest toxic debts racked up by banks and insurers could spiral to $4 trillion, although it gave no sources for the report.
Analysts and traders said while the report fed into the concerns about the banking sector, there was also plenty of reasons to take profits ahead of the U.S. earnings season and investor confidence was still very fragile.
"The currency market has simply been reacting to recent stocks moves. It's too early to say optimism in the market will continue," said Satoshi Okagawa, head of FX forward trading group at Sumitomo Mitsui Banking.
"We need to see upcoming earnings from financial corporations and the results of 'stress tests' among (U.S) banks," he added. (Additional reporting by Charlotte Cooper; Editing by Hugh Lawson)