* Nikkei down 0.6 pct, Topix down 0.5 pct by midafternoon
* Key support at 200-day moving average of 9,903 holds
* Investors shift into defensive stocks, sell banks
* Utilities down after Kansai Electric shuts reactor
* Yen strength puts exporters under pressure
By Antoni Slodkowski
TOKYO, July 19 (Reuters) - The Nikkei stock average fell on Tuesday, moving further away from four-month highs, as banks were sold on growing investor frustration with governments' inability to solve debt crises in the United States and Europe.
A stronger yen, which last week hit a four-month high of 78.45 yen against the dollar on U.S. and European debt woes, pressured exporters.
A four percent decline in Kansai Electric following a shutdown of one of its reactors due to technical glitches on Saturday sent other battered utilities shares lower on worries about tight power supply.
Anxiety about U.S. and European debt woes spurred buying into defensive shares, with Internet companies, retailers and telecomunication firms gaining.
"Investors, worried about the global economy, are again turning to companies with high exposure to the domestic market," said Takashi Aoki, a senior fund manager at Mizuho Asset Management.
The benchmark Nikkei fell 0.6 percent to 9,919.83 by mid-afternoon, with a crucial support at its 200-day moving average of 9,903 breached only briefly in the morning.
The benchmark has been trapped between its 200-day moving average and resistance at 10,000 for over a week as investors ponder their next step, torn between mounting debt woes and relatively strong U.S. corporate earnings suggesting Japanese firms may also post better-than-expected figures towards the end of July.
The broader Topix shed 0.5 percent to 855.15. (Additional reporting by Ayai Tomisawa; Editing by Edwina Gibbs)