Sales at U.S. retailers unexpectedly dropped in May for the first time since September, the Commerce Department said Friday, raising worries that the economy is struggling to recover from the worst financial meltdown since the Great Depression. Americans slashed spending on everything from cars to clothing to building materials, as retail sales plunged 1.2% last month, following a 0.6% April gain that was larger than previously estimated.  It was the largest decline in eight months. Retail sales were projected to increase 0.2% , according to the median estimate of 76 economists in a Bloomberg News survey.