* iPhone disappointment spurs fears of slowing growth * Investors worry about 2013 pipeline * Loses $50 bln of market value after hours as shares tank By Poornima Gupta SAN FRANCISCO, Jan 23 (Reuters) - Apple Inc missed Wall Street's revenue forecast for the third straight quarter as iPhone sales came in below expectations, fueling investors' worries that its dominance of the mobile industry was slipping. Shares of the world's largest tech company fell 10 percent to $463 after-hours, wiping out some $50 billion of its market value from its $514 close. On Wednesday, Apple said it shipped a record 47.8 million iPhones in the December quarter, up 29 percent from the year-ago period but below the 50 million shipments that analysts on average had expected. "It's going to call into question Apple's dominance in the space. It's still one of the strong players, the others being Samsung and Google. It's still a two-horse race, but Android continues to grow rapidly," said Sterne Agee analyst Shaw Wu. "If you step back a bit, it's clear they shipped a lot of phones. But the problem is the high expectations that investors have. Apple's conservative guidance highlights the concerns over production cuts coming out of Asia recently." Apple projected revenue of $41 billion to $43 billion in the current, second fiscal quarter, lagging the average Wall Street forecast of more than $45 billion. Fiscal first quarter revenue rose 18 percent to $54.5 billion, below the average analyst estimate of $54.73 billion, though earnings per share of $13.81 beat the Street forecast of $13.47, according to Thomson Reuters I/B/E/S. Apple also undershot revenue targets in the previous two quarters, and these results will prompt more questions on what Apple has in its product pipeline, and what it can do to attract new sales and maintain its growth trajectory, analysts said. Net income of $13.07 billion was virtually flat with $13.06 billion a year earlier. CHINA IS BRIGHT SPOT Investors' expectations heading into the results had already been subdued by news of possible production cutbacks by some component suppliers in Asia, triggering fears that demand for the iPhone, which accounts for half of Apple's revenue, and the iPad could be slowing. Apple shares are down nearly 30 percent from a record high in September, in part on worries that its days of hyper growth are over and its mobile devices are no longer as popular. Intense competition from Samsung's cheaper phones - powered by Google's Android software - and signs that the premium smartphone market may be close to saturation in developed markets have also caused a lot of investor anxiety. Meanwhile, sales of the iPad came in at 22.9 million in the fiscal first quarter, roughly in line with forecasts. On the brighter side, Chief Financial Officer Peter Oppenheimer told Reuters that iPhone sales more than doubled in greater China - a region that Apple Chief Executive Tim Cook has vowed to focus on as its next big growth driver. The company will begin detailing results from that country. "These results were OK, but they definitely raised a few questions," said Shannon Cross, analyst with Cross Research. "Gross margin trajectory looks fine so that's a positive and cash continues to grow. But I think investors are going to want to know what Apple plans to do with growing cash balance." "And other questions are going to be around innovation and where the next products are coming from and what does Tim Cook see in the next 12 to 18 months."