KABUL, Afghanistan — By now, the billions of dollars spent by the United States on flawed reconstruction projects in Afghanistan have become part of the war’s history. The military headquarters that the Marines did not need, the schools for which Afghans had no use, the road that cost $2.8 million a mile — the list runs long.

In the past year, though, American investigators believe they have found a failed program that may have resulted in the deaths of American soldiers.

The program was intended to keep insurgents from planting bombs in roadside drainage culverts by covering the culverts with thick metal grates. Thousands of the so-called culvert denial systems were supposed to have been installed since 2009.

But investigators say that hundreds, possibly more, were never installed, and that an “investigation is looking into whether this apparent failure to perform may have been a factor in the death or injury of several U.S. soldiers,” according to a report on the investigation. The report was provided to The New York Times before its official release on Tuesday.