U.S. consumer sentiment fell in early September, with people becoming slightly more downbeat about current conditions while worrying that prolonged economic weakness could hurt job prospects and incomes.

The University of Michigan's preliminary September consumer sentiment index fell to 86.2 from a final reading of 87.6 in August, market sources said Friday. That was below economists' forecasts for a reading of 87.5.

Analysts track measures of confidence for clues on future consumer spending, which drives about two-thirds of the U.S. economy. But so far spending, particularly on homes and autos, has stayed robust despite a recent slide in sentiment.

The preliminary September current conditions index, which correlates more closely with consumption patterns, fell to 95.9 from 98.5 in August. The preliminary expectations index, which measures attitudes about the 12 months ahead, edged lower to 80.0 from 80.6 in August.

The preliminary University of Michigan consumer sentiment survey is based on telephone interviews with roughly 300 Americans across the country on personal finances and business and buying conditions. It is rounded out to 500 calls by month's end.