Macintosh and iPod sales helped boost Apple Inc.’s fiscal third-quarter earnings 31 percent, beating Wall Street’s expectations, but investors pummeled the stock after Apple said profit margins contracted and the company issued soft guidance for the quarter.

Cupertino, Calif.-based Apple said Monday it earned $1.07 billion, or $1.19 per share, 11 cents ahead of Wall Street’s expectations, according to a Thomson Financial survey of analysts.

Revenue jumped 38 percent to $7.46 billion, ahead of analysts’ average view for $7.37 billion in sales.

Apple said it shipped more Macs in the quarter than ever before — 2.5 million, up 41 percent from a year ago, with desktop shipments growing faster than laptops. Apple also said iPod shipments jumped 12 percent.

During a conference call, chief financial officer Peter Oppenheimer said sales from U.S. stores rose faster than revenue overall, despite economic turmoil wrought by the domestic mortgage and credit crises.

Steve Jobs, Apple’s chief executive, did not join the conference call with analysts as he commonly does. Apple did not return calls seeking an explanation.

Oppenheimer said in an interview that “the quarter was a home run,” but at first glance, investors disagreed. Shares sank $16.59, or 9.9 percent, to $149.70 in after-hours trading, after gaining $1.34 to close at $166.29.

Investors might have been eyeing that Apple’s gross margin fell to 34.8 percent from 36.9 percent in the year-ago quarter.

Or they could have been spooked that Apple issued a conservative outlook for the current fourth quarter, though the company often does so. Apple predicted profit of $1 per share on $7.8 billion in sales, well short of Wall Street’s expectations. Analysts had been expecting Apple’s fourth-­quarter earnings to reach $1.24 per share on $8.32 billion in sales.