Google shares fell Thursday after quarterly earnings disappointed Wall Street and sharpened worries about the company’s ability to adapt its lucrative business model to increasingly popular mobile devices, where advertising rates are weak.

The company reported revenue of $14.1 billion during the third quarter, up 45 percent compared with the same period last year. But net income fell to $2.18 billion, a decline of 20 percent. Operating costs rose substantially.

The manner of the report’s release made matters worse on Wall Street: It appeared on a Securities and Exchange Web site at midday, several hours before the planned announcement, carrying what appeared to be placeholder text awaiting a quote from chief executive Larry Page.

The combination of the weak numbers and the timing error, which Google blamed on its financial printer, RR Donnelley, pushed the stock price down. Google suspended trading for several hours while it corrected and finalized the earnings report. The stock ended the day down 8 percent, at $695 per share.

Page began the earnings call with analysts by apologizing for the glitch, saying, “I’m sorry about the scramble earlier today.” But he offered an upbeat account of the financial results and the transition to mobile devices, whose smaller screens generate less digital advertising revenue than desktop computers.

“Google is super-well-placed to take advantage of these disruptions,” Page said. He said the company’s overall revenue from mobile devices has grown sharply as smartphones and tablet computers have proliferated.

Analysts, however, focused on the declining rates paid by advertisers per user click. These rates fell 15 percent compared with the same period a year earlier and 3 percent from the second quarter.

Greg Sterling, contributing editor to, said marketers are unwilling to pay as much for digital ads when they appear on mobile devices.

Compared with ads that appear on desktop or laptop computers, where a well-placed pitch often directly leads to a sale on an e-commerce site, mobile users often do research online but make the purchase in person, at a nearby store. That makes it difficult for marketers to know whether their ads are working.

This industrywide problem is not confined to Google, Sterling said, adding that compared with many of its competitors, Google is well-positioned to take advange of growing mobile ad revenue if that market develops.

The company’s Motorola unit hampered overall profit. The business, which makes cellphones and mobile devices, reported an adjusted operating loss of $151 million in the quarter. Google acquired Motorola Mobility for $12.5 billion in May.

Motorola will continue to be a “big negative” for Google as it continues to reduce staff and close offices, said Colin Gillis, an analyst for BCG Partners. “This equation is not going to change any time soon.”

Google is also facing a challenging regulatory situation. European data-protection authorities this week sharply criticized its move to adapt its privacy policy to let it track users across various sites run by the company, such as Gmail, YouTube and the Chrome broswer. It faces antitrust investigations by the European Union and the Federal Trade Commission.

Google executives also blamed currency fluctuations for weaker-than-expected earnings but portrayed the underlying business as healthy and growing. “We had a strong quarter. I’m really happy with our business,” Page said.