About two dozen dump truck owners and drivers testified yesterday that a D.C. Council bill requiring coverings for loaded trucks would do little to reduce debris on city streets while raising substantially the cost of deliveries.

"The debris falls from the tailgates. It doesn't blow off the top," said Thomas J. LaRoque Jr., an independent trucker. "It takes about 10 minutes to put one of these covers on and 10 minutes off. That means I'd lose a load a day -- $50. We'd all have to charge some more."

The bill's sponsor, council member Jim Nathanson (D-Ward 3), said the measure was needed because of the "tens of thousands of accidents and car damage caused {each year} by flying debris . . . in our city's streets." Anne M. Renshaw, a witness at yesterday's hearing, showed the council's Public Works Committee two plastic shopping bags filled with a box, part of a broom, cement powder, and a rusty piece of metal that she said recently fell from trucks in front of her home on Military Road NW.

A truck cover bill was passed last month by the Montgomery County Council, although similar measures have been defeated frequently in the Maryland and Virginia legislatures.