OSAKA (Reuters) - Japan's Nintendo Co. Ltd. cut its first-half operating profit estimate by one third on Friday due to sluggish sales of its GameCube game console and software in the United States, but boosted its net profit estimates due to currency-related gains.

The Kyoto-based company, known for software titles featuring characters such as Mario, Donkey Kong and Pokemon, also cited price cuts to its "DS" portable game machine and high development costs for a new game system as factors weighing on its earnings.

Nintendo said it now expected to book a group operating profit of 20 billion yen for the six months ended September 30, compared to its prior estimate of 30 billion yen.

Yoshihiro Mori, senior managing director at Nintendo, said the biggest negative factor was sluggish sales of software for the GameCube as third-party developers had focused on making games for its next-generation console due next year.

"The big drop for GameCube games was in North America. It looks like the product's (GameCube) life is nearing its end," Mori told a news conference in Osaka, western Japan.

Following the sluggish first-half performance, the game maker slashed its forecast for operating profit in the full year to next March by 22 percent to 90 billion yen and cut its sales forecast by about 4 percent to 500 billion yen.

Margins have also been pinched by hefty development costs for its next-generation "Revolution" console, Mori said. Revolution will hit stores next year and compete with Microsoft Corp.'s Xbox 360, which will launch next month, and Sony Corp.'s PlayStation 3, due for launch next spring.

Mori also blamed the weak operating performance on price cuts to the DS. In August, Nintendo cut the price to $129 from $149 in the United States and this month lowered the price in Europe to 129 euros from 149 euros.

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