* Yen briefly climbs above 84 yen, buoying Nikkei
* Buying of futures by hedge funds leading trade - analyst
* Dec tankan forecast raises hopes for BOJ move - analyst
* Some window-dressing before H1 end also likely
By Elaine Lies
TOKYO, Sept 29 (Reuters) - Japan's Nikkei average rose 0.6 percent on Wednesday as the yen retreated slightly against the dollar after a sharp rise the day before on poor U.S. consumer confidence and rising expectations the Federal Reserve will prepare a fresh round of quantitative easing.
An additional boost may have come from a poor December outlook in the Bank of Japan's "tankan" survey of business sentiment, which some market players said could increase expectations the BOJ will discuss further moves to ease monetary policy at its meeting next week.
Japanese manufacturers' confidence improved for a sixth straight quarter, the survey showed, but they turned negative on the outlook in a sign that yen strength could derail the fragile economic recovery.
"The Nikkei's rising on the slightly weaker yen, and there's also probably some window-dressing ahead of the end of the first half of the business year," said Norihiro Fujito, general manager at Mitsubishi UFJ Morgan Stanley Securities.
"There also may be a slight boost from the December tankan, which was worse than expected, since it suggests there might well be some more easing moves taken by the BOJ."
The benchmark Nikkei was up 54.02 points at 9,551.06 in midmorning, while the broader Topix rose 0.3 percent to 845.04.
The dollar briefly edged back above 84 yen after falling as far as 83.68 yen on electronic trading platform EBS on Tuesday, its lowest since Japanese authorities intervened to weaken their currency two weeks ago.
The Federal Reserve is likely preparing a fresh round of quantitative easing steps to be announced at the end of its Nov. 2-3 meeting, a report by influential hedge fund adviser Medley Global Advisors said on Tuesday, a market source told Reuters.
These expectations grew in the wake of figures showing a decline in U.S. consumer confidence to the lowest level since February, pushing the dollar below 84 yen.
"The outlook for big manufacturers in December looks worse than expected, which is worrying. The strength of the yen is probably the key factor undermining sentiment," said Masaru Hamasaki, a senior strategist at Toyota Asset Management.
"It's possible that the Bank of Japan could take further monetary measures at its next policy setting meeting. It appears that the BOJ thinks it is providing sufficient measures, yet the market doesn't feel that way. The perception gap between the BOJ and the market is still very wide."
Fujito said that much of the action was driven by buying in futures by foreign investors, most likely hedge funds, with virtually no activity by institutional investors.
Exporters edged higher, with Canon Inc rising 0.9 percent to 3,920 yen and Sony Corp gaining 0.8 percent to 2,613 yen.
Shares of Toyo Engineering Corp shot up 5.7 percent to 279 yen after the Nikkei business daily reported it and trading house Marubeni Corp are set to win a contract to construct Mongolia's first oil refinery.
Marubeni rose 1.3 percent to 480 yen.
Elpida Memory Inc jumped 5.4 percent to 960 yen after the company said it would start mass production of advance DRAM chips in December, putting it ahead of bigger rival Samsung Electronics in technology. (Reporting by Elaine Lies; Editing by Chris Gallagher)