* Futures traders place sell orders above 8,800-trader
* Bernanke speech awaited for U.S. easing clues
By Lisa Twaronite
TOKYO, Aug 24 (Reuters) - The Nikkei stock average inched down on Wednesday as investors digested the long-term implications of Moody's Investors Service's downgrade of Japan's sovereign debt rating, erasing gains made earlier on speculation of more U.S. easing.
"Japanese investors shrugged off the downgrade, but some foreign investors used it as an opportunity to lock in gains," in case expectations of more U.S. economic support measures do not materialise, said Toshiyuki Kanayama, a market analyst at Monex Inc.
Stocks also largely shrugged off news of Japan's $100 billion credit line unveiled on Wednesday to facilitate companies' acquisitions of overseas firms and their procurement of energy and resources from abroad, as a step to cope with recent yen strength.
The benchmark Nikkei was down 0.2 percent at 8,714.63 in early afternoon trade, after rising as high as 8,825.27 in the morning session. The broader Topix shed 0.3 percent to 748.44.
On Tuesday, U.S. stocks surged 3 percent on speculation that Fed Chairman Ben Bernanke will signal new help for the economy when he speaks on Friday at the central bank's annual gathering in Jackson Hole, Wyoming.
Traders said that while there are hopes Bernanke will hint at some easing, foreign investors were hesitant to take large positions before the event.
"For the past few days, futures players are thought to be engaged in arbitrage trading. They are trying to make profits within a 100-point range, and today it looks like they were selling when the index rose above 8,800," said a trader at a Japanese brokerage.
NOT UNEXPECTED
Moody's Investors Service cut its rating on Japan's government debt by one notch to Aa3 on Wednesday ahead of the Tokyo open, blaming large budget deficits and a buildup of debt since the 2009 global recession.
Tom Byrne, Moody's senior vice president and regional credit officer, said the agency had no plans to change sovereign ratings for Japan in the next 12-18 months, adding that he saw no change in Japan's home-biased funding dynamics.
Moody's had warned in May that it might downgrade Japan's Aa2 rating due to heightened concerns about its faltering growth prospects and a weak policy response to deal with bulging public debt, now twice the size of its $5 trillion economy.
"Stock market investors had somewhat expected that it could happen because Moody's had warned it might downgrade Japan's sovereign debt earlier," said Norihiro Fujito, senior investment strategist at Mitsubishi UFJ Morgan Stanley Securities.
Unpopular Prime Minister Naoto Kan confirmed on Tuesday he would step down as head of the ruling party within the week.
"We have major developments on the political front, and while most people in the market believe (former foreign minister Seiji) Maehara is very likely to win the (ruling party leadership) election, a swift policy response on debt problems is unlikely to come out soon," said Fujito.
Moody's also took negative action on most Japanese banks as it usually does after a sovereign downgrade.
Some analysts also cited fears about the impact of the Moody's move on lenders' holdings of Japanese government bonds.
Sumitomo Mitsui Financial Group fell 0.5 percent to 2,198 yen in heavy trading.
Mitsubishi UFJ Financial Group dropped 1.8 percent to 336 yen. MUFG was also hit by news that the lender lost $1.8 billion from its common stock investment in Morgan Stanley so far, at least on paper, according to a regulatory filing on Tuesday.
But oil-related stocks outperformed, with Inpex rising 1.1 percent to 474,500 yen and Japan Petroleum Exploration adding 2.3 percent to 3,070 yen. Oil prices rose on Tuesday on views that the Fed might indicate fresh stimulus measures later this week, and also drew support from fighting in Libya and disrupted Nigerian exports.
(Additional reporting by Ayai Tomisawa; Editing by Chris Gallagher)