A closely watched index of future business activity fell in March, a sign that economic growth in the United States may be slowing.

The Conference Board said today that its composite index of leading economic indicators fell 0.4% last month to 115.1.

The decline was slightly larger than that expected by analysts, who had forecast a 0.3% drop in the index.

The March drop followed a rise of 0.1%I n February, and a revised 0.3% decline in January.

There was some good news in the report. The coincident index, an index of current economic activity, increased again in March. The Conference Board says the coincident index has been increasing at a relatively steady 2.5% annual rate since April 2003, and the strength continues to be widespread.

At the same time, the growth rate of U.S. real gross domestic product has been fluctuating around a 4.0% annual rate, including 3.8% in the fourth quarter of 2004.