A juror in the second degree murder and perjury trial of former Washington Abortionist Dr. Robert J. Sherman was excused from the case yesterday after she said that she had received threatening, late night telephone calls, at least one of which was related to the case.

There were indications that the juror, a middle-aged woman, also alleged that some fellow jurors had made statements suggesting they had reached conclusions about the case.

Shortly before noon yesterday, as Superior Court Judge Fred B. Ugast was about to complete a closed door inquiry into the juror's report, Sherman, 65, complaining of chest pains, was rushed by ambulance from the courthouse to the George Washington University Hospital. A spokesman there said late yesterday that Sherman is in fair condition and under observation.

The juror's suden disclosure and Sherman's illness delayed closing arguments in the case, now in its seventh week of trial.

Ugast calld the remaining jurors into the courtroom at mid-afternoon and announced that they would be sequestered in a local hotel for the remainder of Sherman's trial. The juror who reported the telephone calls was replaced by one of three alternate jurors.

The jurors were not told that Sherman had become ill at the courthouse. Ugast said later that Sherman may have to be hospitalized for 48 to 72 hours before doctors can make a "reilable diagnosis" on his condition. Meanwhile, progress in the trial, which had been marked by often dramatic and emotional moments, will be stalled.

Yesterday was the second time in the trial that Ugast has replaced a juror. The juror dismissed yesterday, originally an alternate juror, had taken the place of juror Frieda Hansborough, who was dismissed after she disclosed that she knew a government witness who was about to testify about an abortion procedure she underwent at Sherman's clinic.

It appeared yesterday that the court had not fully resolved the matter of the juror's report, particularly in respect to allegations about statements made by other jurors about the case. Although Sherman is not expected to attend court today, the jury was asked to return to the courthouse at 1:30 p.m.

The events yesterday morning began shortly before attorneys were to offer closing arguments. The juror, visibly shaken, walked into the public corridor outside Ugast's courtroom, and anxiously began to tell a court employe that she had a "problem." The other jurors were in a private room behind the courtroom.

The court employe rushed through the courtroom to find Ugast, who had not yet taken the bench for the day. Moments later, Ugast was heard to tell prosecution and defense lawyers that the juror had told the employe that since last Wednesday she had received threatening telephone calls in the middle of the night about the case.

For the next three hours, Ugast, prosecution and defense lawyers and Sherman sat in a closed, windowless room as the woman and the remaining jurors each were questioned about any telephone calls.

Shortly before noon, as the proceeding was about to end, Ugast said Sherman had said, "I don't feel well. I've got to get up." No jurors were in the room at the time. Ugast called a recess and advised Sherman's lawyers to take him to the courthouse nurse's office.

Ugast returned to his chambers and, minutes later, defense attorney Robert F. Muse rushed in and indicated Sherman was perhaps seriously ill. An ambulance was called and Sherman was carried on a stretcher from the courthouse. An ambulance took him to the hospital. Medication to relieve chest pains and some oxygen were administered in the nurse's office, Ugast said.

A spokesman at George Washington University Hospital said yesterday afternoon that Sherman was admitted to the coronary care unit for observation after initial tests were conducted in the hospital emergncy room. The spokesman said Sherman suffered chest pain due to coronary artery disease.

During pretrial proceedings, Sherman repeatedly complained of a heart condition and at one time w as said to be considering open heart surgery. Before the trial, under Ugast's order, Sherman was examined at the Washington Hospital Center, where doctors reported Sherman's attendance at the trial would not endanger his health.

Ugast said yesterday that he expected to have word from the hospital by Wednesday morning on Sherman's condition. Sherman is charged with murder in connection with the death of 16-year-old Rita McDowell, who died at the D.C. General Hospital on March 8, 1975, four days after she went to Sherman's clinic in northwest Washington for an abortion. Sherman is also charged with 25 counts of perjury in connection with what the government contends were false statements made about McDowell's treatment and conditions at Sherman's clinic.