D.C. Superior Court Judge Fred B. Ugast is expected to rule today on a defense motion for a mistrial in the second-degree murder and perjury trial of former Washington abortionist Dr. Robert J. Sherman.

Meanwhile, Sherman, 65, was reported in fair condition at George Washington University Hospital, where he was admitted Monday after he complained of chest pains. A hospital spokesmand said Sherman may be released from the hospital today depending on the outcome of additional tests related to heart problems.

Defense attorney Robert F. Muse adked Ugast to declare a mistrial Wednesday because he said recent unexpected events in the case, including Sherman's illness, the replacement of a juror and Ugast's decision to sequester the entire jury, could adversely affect the jury's deliberations in the case.

Closing arguments had been scheduled for last Monday but were abruptly delayed when a juror-who was later excused from the case-told the judge that she had received threatening telephone calls, one of which was related to the case. At about noon Monday as Ugast was completing an inquiry into the juror's report, Sherman said he was ill and was rushed by ambulance to the hospital.