A key gauge of future economic activity fell for the third month in a row in March, showing that the recession may persist through the summer, a nonprofit research group said on Monday.

The Conference Board's Leading Economic Index declined 0.3 percent last month, much steeper than the 0.2 percent analysts polled by Reuters were expecting. It also fell 0.2 percent in February, which was originally reported as a 0.4 percent drop.

The recession may continue through the summer, but the intensity will ease, said Ken Goldstein, an economist at the Conference Board, in a statement.

The index has not risen once in the last nine months. In September and December it was unchanged and it experienced the largest drop in October, when it fell 1.0 percent.

Real money supply and the yield spread both showed strength in March, but not enough to counterbalance the drag of building permits, stock prices and supplier deliveries.

Over the last six months, the index fell 2.5 percent, compared to the smaller 1.4 percent drop for the previous six months.

(Reporting by Lisa Lambert, Editing by Chizu Nomiyama)