Americans gave automakers a confidence boost in January. They bought more cars and trucks and showed a still-fragile auto industry that they were ready to replace their clunkers in 2011.

Sales of cars and light trucks in the United States rose 17 percent from a year earlier to 819,895. That’s still below the 1 million sold in January 2008, before most people felt the impact of the recession, but better than the last two years, when January sales fell below 700,000.