A former top legal adviser to U.S. Attorney General Dick Thornburgh is the target of a federal investigation of alleged cocaine use by public officials and professionals, sources said Thursday. Henry G. Barr of Mechanicsburg, who was general counsel when Thornburgh was governor and later was an assistant to Thornburgh when he became attorney general, is being investigated by the same grand jury that has been hearing evidence about alleged cocaine use and distribution by Richard Guida, a former top deputy in the state attorney general's office, the sources said. The sources, including several lawyers close to the case who were interviewed independently, said Barr's attorneys were in Washington earlier this week asking the Justice Department to block an indictment that would name Barr. In Washington, Justice Department spokesman Dan Eramian said Thornburgh and members of his personal staff withdrew from the federal investigation when they learned of its existence earlier this year. Eramian added that Thornburgh had no knowledge of the drug issue when he was governor. The sources also said Guida has agreed to plead guilty to one count of using cocaine and to cooperate with the federal investigation. Under the agreement, they said, Guida could face a short jail term and suspension of his law license. The sources spoke on condition of anonymity because grand jury proceedings are supposed to be secret. According to court documents, Guida has been a target of the federal investigation since May. The grand jury's attention turned to Barr more recently, the sources said. Barr did not return telephone messages left on the answering machine at his Mechanicsburg home Thursday. Guida did not return messages left at his Harrisburg law office. In previous interviews, he denied using cocaine and being a target of the probe. Assistant U.S. Attorney Gordon Zubrod declined to comment because of a policy that prohibits federal prosecutors from confirming or denying details of investigations. By being allowed to plead guilty only to a possession charge, Guida would sidestep allegations that he also sold cocaine and provided it to friends. At least one witness, Brenda Snell of suburban Harrisburg, said in an interview with The Associated Press that she told the FBI she had purchased cocaine from Guida and sold it to him on several occassions. Guida called those allegations ``bold-faced lies.'' This is the second time cocaine allegations against Guida have been investigated. In 1986, when he was a chief deputy under state Attorney General LeRoy S. Zimmerman, an internal probe found no evidence to support a radio reporter's allegations that Guida was a user. State Attorney General Ernie Preate Jr. said Thursday he would not investigate allegations that the initial probe was a whitewash because the federal grand jury also was looking at that aspect of the case. Barr, 46, worked in the state attorney general's office before joining Thornburgh's gubernatorial administration. He became Thornburgh's general counsel about 18 months before the governor left office in 1987. In Washington, he served as a special assistant to the attorney general from September 1988 to May 12, 1989. Last year, he resumed a private law practice in Harrisburg, but quit earlier this year after allegations surfaced that connected him to the case, the sources said. Barr and Guida each served as deputy attorney general in charge of the state attorney general's criminal division. Barr also served as an assistant U.S. attorney in Pittsburgh from 1969 to 1979. Through much of that period, Thornburgh was the U.S. attorney in western Pennsylvania. The grand jury investigation has lasted nearly a year.