About one-sixth of the books, monographs and bound periodicals at the Library of Congress weren’t where they were supposed to be because of flaws in the systems for shelving and retrieving materials, according to a survey to be made public at a congressional hearing today.

Officials at the library say they believe most of the missing materials are misplaced, not stolen or lost.

Investigators for the congressional library have told lawmakers on a House oversight committee that its review of the retrieval system for the general collection concluded that 17 percent of materials requested could not be found.

“A subsequent review found 4 percent were either on nearby shelves, checked out to the public or marked with the wrong call numbers. But it remains deeply troubling that nearly 13 percent are unaccounted for by library officials,” said Howard Gantman, staff director of the joint congressional committee on the library.