U.S. Attorney Earl J. Silbert, in a sharply worded memorandum has disputed a D.C. Superior Court judge's finding that a prosecutor had acted improperly in inquiring about a defense witness during the second-degree murder trial of former Washington abortionist Dr. Robert J. Sherman.

Judge Fred B. Ugast declared a mistrial in the lengthy case last Dec. 15 after a juror's report that she had received threats caused delays in the proceeding.

Sherman, who was charged with performing an incomplete abortion on a 16-year-old patient that led to her death four years ago, is scheduled to stand trial again this month. Sherman, 65, is also charged with various counts of perjury.

During the trial, Robert F. Muse and Constance O'Bryant, Sherman's attorneys from the city's Public Defender Service, told Ugast that some defense witnesses complained they had been intimidated and harassed by government prosecutors and district homicide detectives prior to their testimony.

The defense also charged that a key expert witness, Dr. Thomas Gresinger, ahd been threatened with economic reprisals if he testified for Sherman. Defense attorney Muse contended that those statements to the witness followed telephone inquiries made by Assistant U.S. Attorney Whitney S. Adams to associattes of Gresinger. Adams and principal assistant U.S. Attorney Carl S. Raygh, prosecuted the case for the government.

The government vigorously disputed the defense contentions. Ugast, however, told the government that police should identify themselves only as calling on behalf of the U.S. attorney's office-not the homicide squad-and sternly reprimanded Adams. Ugast said Adams had exercised "extremely poor judgment" in the telephone inquiry when she failed to tell the persons she contacted not to talk to Gresinger.

In his memorandum, which was filed in Superior Court Tuesday, Silbert argues that Ugast had no legal authority to issue the order on police identifications. Silbert also said that Ugast's comments about Adams were "completely unfair." Silbert also contended that Adams had no authority to instruct the persons she talked with about Gresinger not to contact the defense witness.