THE CLICKS, pops and pings you hear as bouncing pebbles assail your car's windshield and fenders aren't necessarily the fault of that dump truck rolling along in front of you with a full load of gravel. That, at least, has been one of the arguments made over the years by trucking lobbies, which say that much of the stuff that strikes cars is kicked up from the road by the tires of other vehicles.

It isn't a very convincing argument, nor are most of the others made by truckers in their long battle against laws that would require dump-truck operators to cover their loads. But in Maryland, the lobbyists haven't had to convince that many people. For a quarter of a century the cover-up bills, heavily lobbied by truckers, have been killed in committee; they've become something of a long-running legislative joke.

This week the Montgomery County Council, despairing of the state's ever acting on the problem, enacted its own truck-cover law (by a 6-to-0 vote). It will apply only to county roads, but most dump trucks find it necessary to use these lesser traveled roads at some time in their working day. Perhaps, too, the effect will spread to neighboring jurisdictions as trucks going to and from Montgomery put on covers. Meanwhile, there is talk of introducing a similar bill in Howard County, Montgomery's neighbor to the north.

Bouncing debris on Maryland roads causes more than $5 million a year in damage to windshields alone, according to the American Automobile Association. More important, it's dangerous. Montgomery's new law faces challenges in court, on the grounds that this is an area of regulation the state has reserved to itself. But even if the law is overturned, it will have been worth the effort if it helps prod the General Assembly into long overdue action of its own.