* Chubu Electric rebounds on short-covering -traders * Nikkei resistance may hold firm at 9,900 this qtr -analyst By Ayai Tomisawa TOKYO, May 10 (Reuters) - Japan's Nikkei stock index edged down on Tuesday, hurt by a cut in Greece's credit rating that outweighed gains in commodity-linked stocks on the back of higher gold and oil prices. Investors remain largely on the sidelines ahead of more corporate earnings from major companies, including bellwether Toyota Motor , which reports on Wednesday. Standard and Poor's cut Greece's rating to B from BB-, dragging it further into junk territory on concerns a debt restructuring is increasingly likely. Moody's threatened to cut the country's ratings by several notches. [ID:nLDE7480MK] "The impact from Greece's downgrade is not that big, but it is not helping investor appetite," said Fujio Ando, senior managing director at Chibagin Asset Management. "If companies like Toyota do not release forecasts for this financial year, resistance for the Nikkei may hold firm around 9,900 until there are more signs of a recovery in earnings later this year." The benchmark Nikkei average dropped 0.2 percent to 9,771.11, while the broader Topix also shed 0.2 percent to 851.97. Toshiba Corp gained 3.5 percent to 450 yen in active trade after Japan's biggest chipmaker said it expects its operating profit to rise by 25 percent in the year to March 2012, roughly in line with market expectations, though it warned that potential power outages could jeopardise that outlook. [ID:nL3E7G90R0] Commodity-linked shares outperformed, with trading house Mitsubishi Corp gaining 0.6 percent to 2,184 yen and Inpex adding 0.4 percent to 574,000 yen after gold and oil prices rose. Chubu Electric recouped some big losses made the previous day, adding 2.2 percent to 1,619 yen, after it agreed to shut down its nuclear plant until it can be better defended against the type of massive tsunami that in March triggered the worst atomic crisis in 25 years.[ID:nL3E7G90WG] Chubu shares tumbled 10 percent on Monday, but market players said retail investors encouraged by the stock's high dividend yield covered some of their short positions on Tuesday. Shares in Japanese shipbuilder Sumitomo Heavy Industries surged 13.0 percent to 603 yen after the company said it expected its annual operating profit to increase 18 percent to 54 billion yen ($673 million) and after Goldman Sachs hiked its target price for the firm to 680 yen from 650 yen. (Additional reporting by Antoni Slodkowski; Editing by Edwina Gibbs)

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