* Asian shares ex-Japan up 0.2 pct, Nikkei jumps 1.5 pct
* Aussie dollar bounces off 4-1/2 month low
* Rupiah, peso, baht come under pressure
* Fed to issue policy statement at 1900 GMT
TOKYO, Dec 18 (Reuters) - Asian shares tiptoed higher on Wednesday as investors waited to hear when the U.S. Federal Reserve will begin unwinding its stimulus campaign, a major driver for global risk assets in recent years.
On Tuesday, a better-than-expected report on U.S. house builder confidence and inflation data suggesting low but stable price growth, supported the view that economic conditions are adequate for the U.S. central bank to start scaling back its $85 billion monthly bond-buying.
A majority of economists polled by Reuters expect the taper to happen in March, but a recent run of upbeat economic data has steadily shortened the odds on a taper announcement at the end of the Fed meeting later in the day -- or in January.
"The market-neutral decision is a January taper," Citigroup said in a note. "A nominal taper (on Wednesday) would catch 60 percent of the market by surprise -- and FX positioning remains overweight emerging market FX."
"For traders, this is still U.S. dollar-positive, but the sustainability of USD strength depends on any language changes we expect to accompany it."
The Federal Open Market Committee will release a policy statement at 1900 GMT, followed by Fed Chairman Ben Bernanke hosting a keenly-awaited news conference a half hour later.
MSCI's broadest index of Asia-Pacific shares outside Japan inched up 0.2 percent, though still faced resistance at its 200-day moving average. On Tuesday, it trimmed early gains to end flat.
Japan's Nikkei share average, spurred by buying from hedge funds, climbed 1.5 percent, extending Tuesday's rebound from a sharp loss in the beginning of the week.
The Nikkei benchmark has risen 49 percent this year, on track to its best yearly rise since 1972, powered by Tokyo's aggressive fiscal and monetary stimulus to revive the world's third-largest economy.
Overnight, U.S. stocks closed slightly lower, with the Standard & Poor's 500 down 0.3 percent, as investors were reluctant to make big bets before the Fed decision. S&P 500 E-mini futures added 0.1 percent in Asian trade on Thursday.
As the Fed decision loomed, Indonesia's rupiah fell to a near five-year low of 12,155 per dollar, while the Philippine peso dropped 0.3 percent to 44.28 to the dollar, hitting a one-week low, and the Thai baht eased 0.2 percent to 32.17.
But with the Nikkei rallying, the dollar bounced 0.3 percent to 102.93 yen, having fallen 0.3 percent overnight. The greenback hit a five-year high of 103.925 yen on Friday.
"We may see nothing at all from the Fed, although they would give a strong indication a taper is on the cards. This is a strong possibility as well, which could be USD negative," Chris Weston at financial spreadbetter IG wrote in a note.
"I would use this as a buying opportunity though, especially against the JPY, given the market will start to expect this action in January."
The euro was steady at $1.37720, having risen 0.2 percent in the previous two sessions. The common currency touched a six-week high of $1.3811 on Dec. 11.
The Australian dollar was up 0.2 percent at $0.8917, coming off a 4-1/2 month low of $0.8882 set on Tuesday after the country's central bank reiterated its recent message that the currency was uncomfortably high.
Among commodities, U.S. crude prices added 0.2 percent to about $97.4 a barrel, recovering from the previous session's 0.3 percent decline.
Gold rose 0.4 percent to around $1,234 an ounce, having fallen 0.8 percent overnight. The precious metal has fallen more than 26 percent this year, heading for its worst annual performance since 1981.