US truck tonnage index slips in April-ATA

* Tonnage hauled down 1.1 pct in April vs March

* First decline after seven months of gains

* April 2012 level up 3.5 pct versus April 2011

May 22 (Reuters) - The index tracking tonnage hauled by American trucks slipped in April compared to March, snapping seven straight months of gains, dragged lower by slowing growth in the wider economy, the American Trucking Associations said on Tuesday.

The advanced seasonally adjusted for-hire truck tonnage index however was up 3.5 percent in April against year-ago levels.

The index fell 1.1 percent in April compared to the previous month, after revised data showed a 0.6 percent increase for March over February. Initial estimates released last month which showed 0.2 percent growth for March.

"While April's decrease was a little disappointing, the March gain turned out to be stronger than originally thought," ATA Chief Economist Bob Costello said.

"While just one month, the April's decrease also matches with an economy that is likely to grow slightly slower in the second quarter than in the first quarter."

Costello added that annual growth of 3 to 3.9 percent was expected for 2012, down from the 5.8 percent growth seen in 2010 and 2011. So far this year, tonnage has risen by 3.8 percent compared with 2011.

The non-seasonally adjusted index dipped 5.5 percent in April compared to March. (Reporting by Matthew Robinson; Editing by Bob Burgdorfer)