WASHINGTON (AP) _ The FBI says it dropped an investigation into a convicted murderer's allegations that the bodies of black people killed by the Ku Klux Klan were buried in a mass grave in Fauquier County, Va.

The case was closed after the Nevada inmate who made the allegations, Edward Allan See, 43, failed a polygraph test this week, authorities said Thursday.

FBI officials began looking into the claims in February after See, who is serving two consecutive life sentences at Ely State Prison, told them 50 people were buried in the Warrenton area, 45 miles southwest of Washington.

See, who failed part of a polygraph test administered by the FBI in March, also flunked the second test, which was administered Tuesday at Ely, authorities said.

''Based on that information we received today, we have discounted the information provided by Mr. See to date and no further investigation will be done,'' said Thomas F. Jones, FBI public affairs chief. ''A second polygraph was given and an evaluation and review of that led us to believe that no further reaction is required in this matter.''

William F. Dwyer, a Beverly Hills, Calif., attorney who represents See, said he was disappointed by the FBI's decision. He urged the bureau to verify or discredit See's claims by excavating the alleged grave site.

He also said See wanted an independent polygraph test.

''If the FBI has chosen to close the investigation based on Eddie See's polygraph examination, then it appears sweat (affecting the polygraph) is considered more reliable than a backhoe in unearthing what may or may not be buried remains of Klan killings,'' Dwyer said.

See claims he participated in the killings of several blacks abducted from the Washington area, tortured and killed. He says he was a member of the Klan from 1961 to 1964.