* Market optimism gives way to caution, lifting yen, dollar
* BOJ keeps rates steady, expands assets used for market ops
* RBA holds rate meeting, close call on whether it will cut
By Charlotte Cooper TOKYO, April 7 (Reuters) - The yen and the dollar climbed on Tuesday, benefiting from defensive position-taking as a flush of optimism that powered a recent rally in stocks and higher-risk currencies gave way to caution about banks.
Traders said the decline in the euro and higher yielding currencies was also driven by profit-taking after the single European currency and the dollar rose to their highest in nearly six months on the yen on Monday.
The Australian and New Zealand dollars, which have both ridden higher on improving risk appetite, also retreated from recent multi-month highs, with the market keen to see whether Australia's central bank cuts rates on Tuesday.
The Bank of Japan (BOJ) kept its rates steady at 0.1 percent as expected, leaving the market free to focus on the Reserve Bank of Australia, where a decision was due at 0430 GMT.
The market is keen to see if the RBA trims interest rates by 25 to 50 basis points or keeps them steady at a record low of 3.25 percent.
"The market is completely divided on this one," said Sue Trinh, senior currency strategist at RBC Capital Markets in Sydney.
"The bottom line is that there will be a huge amount of volatility on the Aussie dollar on the announcement, with the market pricing in a little over 25 basis points worth of cuts."
The Aussie slid 0.3 percent to $0.7100 and 0.8 percent to 71.38 yen, after leaping to a six-month high of 72.87 yen on Monday, according to Reuters data.
The BOJ unveiled further steps to ease credit strains, as the the world's No.2 economy wallows in its worst postwar recession amid a global credit crisis.
It 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.
SHORT-TERMISM
The euro fell 0.4 percent on the day to $1.3358 and 0.8 percent to 134.38 yen, after touching 137.42 yen on Monday, its highest since late October.
The dollar also slipped against the yen, falling 0.4 percent to 100.53 yen ahead of the BOJ decision and staying there afterwards. It had climbed to 101.45 yen on Monday.
Trinh said the dollar 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.
But against a basket of major currencies it was up 0.2 percent and clawing back ground against sterling.
A fall in European and U.S. shares on Monday on renewed worries about the health of banks and the collapse of IBM's takeover bid for Sun Microsystems fuelled profit-taking on the euro, Aussie and the New Zealand dollar.
"It's a tendency since the financial crisis for investors to be risk averse, and they don't hold positions for a long time. As a result the theme in the market changes every week," said Toru Umemoto, chief FX strategist at Barclays Capital in Tokyo.
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 the report fed into the revival in concerns about the banking sector, although there was also plenty of reason to take profits on the recent rally ahead of the U.S. earnings season.
"The market in Asia is largely driven by players' correction on recent rapid gains in pairs such as euro/yen and dollar/yen," one trader said. (Editing by Hugh Lawson)