Secret Service supervisors shared crude sexual jokes and engaged in racially derogatory banter about blacks, and passed around an anecdote about a possible assassination of the Rev. Jesse Jackson, according to internal e-mail disclosed in a federal court filing on Friday by lawyers for black Secret Service agents.

The filing includes 10 e-mail messages that were among documents the agency recently turned over to lawyers for the black agents as part of an increasingly bitter discrimination lawsuit. The messages were written mainly from 2003 through 2005, and were sent to and from e-mail accounts of at least 20 Secret Service supervisors.  The messages offer a glimpse into the darker recesses of an agency known for protecting presidents and other dignitaries but whose culture is regarded as one of the most insular in federal law enforcement. The disclosure of the messages follows an incident last month in which a noose was found in a room used by a black instructor at a Secret Service training facility in Beltsville, Md. Agency officials said that episode was under internal investigation.