DEARBORN, Mich. — Ford Motor Co. is the most profitable it’s been in a decade, since the days when Americans were snapping up SUVs. But maintaining that momentum – and meeting the high expectations of buyers, workers and investors – will be a big challenge in the coming year.

Ford got a taste of that Friday. Despite reporting a profit for 2010, the company’s stock fell more than 13 percent to close at $16.27. Investors were disappointed that the results fell short of expectations. Ford also posted an 80 percent drop in fourth-quarter net income, missing forecasts and ending two years of better-than-expected results.

It was clear that Ford won’t have much room for error as it tackles nagging problems, from the huge loans it took out to fund its turnaround to its upcoming labor talks to its stodgy, slow-selling Lincoln brand.

“When a company consistently beats expectations, analysts and investors start pushing. They raise the bar to the extent that eventually they’re going to miss it,” Standard and Poor’s analyst Efraim Levy said.

Ford earned $6.6 billion, or $1.66 per share, last year, more than double the $2.7 billion, or 86 cents per share, it made in 2009. That was the most it’s made since 1999, when it earned $7.2 billion.

But excluding charges from debt reduction and other items, Ford earned $1.91 last year, below the $2.05 analysts expected. Ford said it should have kept analysts better informed about potential problems in the fourth quarter, including a loss in Europe and a $1 billion increase in costs in North America, partly to fund the launch of new products like the Ford Explorer.

By any measure, Ford has made big improvements since CEO Alan Mulally joined the company in 2006. Ford sold or shuttered five of its seven brands, closed or sold a quarter of its plants and cut its global work force by more than a third. It also slashed labor and health-care costs, plowing the money back into the design of well-received new products such as the Ford Fusion sedan and Ford Edge crossover.

As a result, a leaner Ford was in a good position to scoop up U.S. market share when its Detroit rivals, General Motors and Chrysler, filed for bankruptcy protection in 2009 and when Toyota announced a damaging series of safety recalls last year. Ford’s U.S. sales jumped 20 percent in 2010, double the rate of the rest of the industry. The Ford brand was the top-selling brand in the U.S. last year, besting Chevrolet and Toyota for the first time since 2003.