CHICAGO, July 25 (Reuters) - Harley-Davidson Inc posted a higher quarterly profit on Thursday, lifted, in part, by a modest rebound in demand for its motorcycles in the United States, its No. 1 market. The Milwaukee-based company reported a second-quarter profit of $271.7 million, or $1.21 a share, up from $247.3 million, or $1.07 a share, a year ago. Sales rose 3.4 percent to $1.79 billion.