HOOVERTOWN, W.Va. (AP) _ A Chessie System freight train on the wrong track slammed into camp cars used to house railroad workers Tuesday, injuring 21 people, officials said.

''A wrong switch must have been pulled to put the freight train on the same track,'' said Richard Bussard, a spokesman for CSX Transportation Corp., Chessie's parent company. ''It should not have been on that track.''

Some of the injured railroad workers said they were asleep when the accident occurred shortly before 7:30 p.m., said William Ryan, associate administrator at St. Joseph's Hospital in Buckhannon, where 21 people were taken.

One man was admitted for back injuries and another was being held for observation, said Ryan. He described most of the injuries as ranging from neck and back injuries to ''a lot of bumps and bruises.''

Three locomotives and six of the 36 camp cars derailed, and one of the locomotives overturned, said Bussard.

The side track was a regional collection area for camp cars, where railroad workers live while in the field on construction projects, said Bussard.

The freight train was pulling 31 cars, 12 of them empty, he said.

The derailed train blocked the main road through Hoovertown, said Buckhannon firefighter Jerry Wilfong