Defense attorneys of former Washington abortionist Dr. Robert J. Sherman asked a D.C. Superior Court judge yesterday to declare a mistrial because sudden developments in the case since Monday, including Sherman's hospitalization and the replacement of a a juror, threaten Sheman's guarantee of a fair trial.

Attorney Robert F. Muse expressed concern that the jury's judgement of the case might be clouded - and Sherman prejudiced - by the doctor's absence from the proceedings, that the jury was unexpectedly sequestered Monday, at the start of the seventh week of trial.

Muse noted that the jury had received no explanation about the developments. "All the speculation inherent in such a situation grows," Muse told Judge Fred B. Ugast and could result in prejudice against Sherman. Ugast said he would rule on the mistrial motion this afternoon.

A juror was excused from the case Monday after she reported to the court that she had received threatening telephone calls since Dec., 6, at least one of which was related to the case. There was information that the juror also alleged that some fellow jurors had made statements indicating they had reached conclusions about the case.

At noon Monday, Sherman was taken from the courthouse by ambulance to George Washington University Hospital, complaining of chest pains. Ugast said yesterday that doctors had told him that Sherman may be able to return to court on Saturday.

Principal Assistatn U.S. Attorney Carl S. Rauh opposed the mistrial motion and argued the jurors seem "relaxed and prepared to fulfill their civic responsibility" and complete the case. Rauh said there was "no anything other than deliberate fairly."