The company didn’t sell as many iPhones as Wall Street was hoping for in the recent quarter, a period during which co-founder Mr. Jobs handed the reins to new Chief Executive Tim Cook. Mr. Jobs died after a long battle with pancreatic cancer earlier this month.

Apple said Tuesday it sold more than 17 million iPhones in its fiscal fourth quarter ended Sept. 24, up from more than 14 million a year ago but lower than the 20 million or more that analysts had been expecting.

Apple’s shares, which have been climbing to record highs recently, dropped 6.5%, or $27.43, to $394.81 in after-hours trading Tuesday following the results.

Mr. Cook, speaking on a conference call, said iPhone sales slowed toward the end of the quarter amid speculation over the debut of a new model. Mr. Cook was optimistic about the new iPhone 4S, which Apple began selling on Friday after the quarter closed.

We are “very confident that we will set an all-time record in the December quarter for iPhone sales,” he said.

The results show how important the iPhone franchise has become to the Cupertino, Calif., company, just as competition in the smartphone arena intensifies—and how the unrelenting buzz around the company’s new products can come back to bite it. In recent quarters, the iPhone has contributed more than a third to nearly half of Apple’s revenue, according to analysts, and its business depends on consumers continuing to buy or upgrade to new versions of the more than four-year-old device.

Some analysts said the results shouldn’t be seen as too negative. “We don’t think this is a slowdown in [market] share gains, it’s a pause,” said Brian Marshall, an analyst ISI Group.

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