DEARBORN, Mich. — Just three years after Ford revived its American business, the company must pull off an even trickier turnaround in Europe, where mounting losses weighed down its quarterly results.

Ford’s second-quarter net income fell 57 percent to $1 billion, largely because of a $404 million loss in Europe. Car sales there have tumbled to 20-year lows because shoppers are worried about the region’s debt crisis and economic slowdown. Ford expects to lose more than $1 billion in Europe in 2012, double its estimate from the beginning of the year.