Nokia, the world's largest cell phone maker, reported a $1.36 billion loss in the third quarter on Thursday as it wrote down the value of its wireless networks venture by $1.35 billion and global sales declined 20 percent. The company said that its leading share of the global cell phone market remained unchanged at 38 percent. But it acknowledged that its lead in smartphones, the fastest-growing segment of the market, had fallen to 35 percent, from 41 percent, losing ground to Apple's iPhone and Research in Motion's BlackBerry devices. Nokia's quarterly loss was in contrast to a profit of $1.63 billion a year earlier. Analysts said Nokia was being hurt by the slowing global economy, ferocious price competition and a weak portfolio of smartphones. 'Apple and RIM are really starting to eat into Nokia's lead in smartphones,' said Jan Dworsky, an analyst at Handelsbanken Capital Markets in Stockholm. Nokia said the average sale price for one of its mobile phones fell 14 percent, to $92, from $107 a year earlier. The company's operating margin for the phones, basically its profit before taxes, fell to 11.4 percent, from 12.2 percent in the second quarter and 18.6 percent a year earlier. Stock in Nokia, which is based in Espoo, Finland, fell 11 percent. 'The big drop in Nokia's operating profit margins, coupled with the significant loss in market share for smartphones, is what the market is really concerned about,' Dworsky said. In a statement, Olli-Pekka Kallasvuo, Nokia's chief executive, noted that the company had sold more cell phones in the third quarter than in the second quarter and said that the continuing problems at Nokia Siemens, the wireless network venture with Siemens of Germany, were a result of 'challenging competitive factors and market conditions.' 'We continue to support Nokia Siemens Networks' actions to improve its performance,' Kallasvuo said. The write-down at Nokia Siemens pushed that venture, which started in April 2007, to an operating loss of $1.6 billion in the third quarter, compared with a loss of $1.4 million a year earlier. Overall, Nokia's sales fell to $14.5 billion in the third quarter, from $18.1 billion a year earlier, hurt by declines of 25 percent to 31 percent in Latin America and North America, and the Asia-Pacific and Middle East-Africa regions. 'It's obviously tough times in the industry,' said Chris Jones, an analyst at Canalys, a research business in Reading, England. 'There is huge price competition in the mobile phone market, and Nokia is trailing its rivals, particularly Apple and RIM, in the race to make easy-to-use and fun smartphones.' Jones said Nokia Siemens was losing network equipment business to low-cost Chinese makers Huawei Technologies and ZTE Corp., whose gains in Europe and Asia have also caused problems for Alcatel-Lucent, the Paris-based equipment maker. 