WASHINGTON — The primary U.S. juvenile justice law, the 1974 Juvenile Justice and Delinquency Prevention Act (JJDPA), would undergo its first major overhaul in two decades under a bill to be introduced this week. Sen. Charles E. Grassley, R-Iowa, the chairman of the Senate Judiciary Committee, announced the impending introduction of the bipartisan measure, co-sponsored by Sen. Sheldon Whitehouse, D-R.I., at a news conference at the National Press Club today. The JJDPA had originally been designed to protect youths in trouble with the law, preventing them from being housed with adult criminals, for instance. It was also meant to reduce racial and ethnic disparities in juvenile justice and bar detention of children for “status offenses” like skipping school. Status offenses are so named because they’re crimes only by virtue of the offender’s status of being a juvenile.