A D.C. Superior Court judge declared a mistrial yesterday in the case of former Washington abortionist Dr. Robert J. Sherman, who was charged with second-degree murder and perjury in the death of a 16-year-old abortion patient more than three years ago.

When he announced his decision, Judge Fred B. Ugast said he feared that the court's private questioning of each juror earlier this week-prompted by a juror's report that she had been threatened-and the delay that followed may have impaired the evidence.

With that, Ugast brought an end to an unusually long and emotional trial that was marred over seven weeks with dramatic interruptions, including charges that defense witnesses had been threatened, jury hospitalization Monday.

The mistrial ruling itself was followed by yet another bizarre twist in the case when a government prosecutor stood in court and accused Sherman of "faking" his illness, and disclosed allegations that Sherman had ordered a drug from a pharmacy that would have adversely affected the outcome of hospital tests and thus prevented his return to court.

Ugast then encouraged Principal Assistant U.S. Attorney Carl S. Rauh to file court papers to require Sherman, 65, to explain why he should not be held in contempt of court for allegedly trying to interfere with the tests.

"If Sherman did contribute to these unfortunate delays it should be dealt with appropriately," Ugast said, ". . . but the fundamental aspects that I found in doubt would not be altered by this."

Ugast, visably distressed by the outcome of the case, then called the jury of seven women and five men and two alternates into his courtroom and told them that because of delays in the case and the impending Christmas holiday, he was going to declare a mistrial in the case.

"I have found you ready, willing and able to do the job," Ugast explained to the somber panel. But, he said, after much "soul searchin" he had decided to end the case.

Rauh told reporters outside the courtroom that the government would prosecute Sherman again. A hearing on the case was scheduled by Ugast for Jan. 16.

When he declared the mistrial, Ugast said he was "painfully aware of the "time, effort and expense" that had been invested in the case, which began with jury selection on Oct. 24. Rauh and Assistnat U.S. Attorney Whitney Adams brought the case for the government after a long investigation into the death of 16-year-old Rita McDowell, who died at D.C. General Hospital on March 8, 1975, four days after she went to Sherman for an abortion.

Sherman, who was declared indigent by the court, was represented by Robert F. Muse and Constance O'Bryant, both attorneys with the city's Public Defender Service, which is funded by the city governmebt.

The turning point in the case came Monday morning, as prosecution and defense lawyers were about to begin closing arguments. in the case. A woman juror walked into the public corridor outside Ugast's courtroom and suddenly informed a court employe that she had received threatening telephone calls about the case.

That prompted Ugast to begin his closed-door inquiry of each juror. There were also indications that the woman juror informed the court that some jurors had reached conclusions about the evidence in the case.

It was during that inquiry, in a small, windowless room, that Sherman compalined of chest pains. He was later rushed by ambulance to George Washington University Hospital. He was released from the hospital late yesterday after medical tests for heart problems proved negative.

Sherman has some history of heart problems. Defense attorney Muse told Ugast yesterday-in response to the government's allegations-that Sherman's illness was not "feigned" and that his condition required careful observation.

Following the juror's report Monday, Ugast excused her from the case but decided to continue questioning the remaining jury members about the nature of the report. He also ordered that the jury be sequestered for the remainder of the trial.

Ugast said in court yesterday that he felt compelled to conduct the inquiry because of the "very serious nature of these allegations." But, he said, after considering the questions asked, the juror's responses and their demeanor during the procedure, he had "grave doubs" about whether th questioning itself "has not impermissibly intruded on the jury."

Ugast indicated he wanted to make it clear that during his inquiry, he found no facts to support the single juror's allegations that fellow members had violated the court's instruction not to reach conclusions about the case until the trial was completed.

But even careful questioning may have elicited information that pierced the confidence and secrecy of the jury and might cause some jurors to feel "some sense of subtle coercion because we know some of the things we know," Ugast explained.

That might cloud the "fundamental fairness" of the jury's deliberations, Ugast said, "not because of anything the jury has done but because of all that has happened."

Moreover, Ugast said, the lapse of time between the close of the defense evidence and the start of jury deliberations posed a "serious problem."

The jury members might give "undue weight" to strong testimony from key experts for the government who were called to counter the defense evidence as the last witnesses in the case. Ugast noted that the jury had heard the completion of the defense evidence on Dec. 1, while the government's rebuttal witnesses completed their testimony on Dec. 7.

Again, Ugast said he was concerned about the jurors' ability to fairly decide the evidence as a result of the delays. His cocer, Ugast said, arose because the jurors are "simple human beings place in a very difficult situation unavoidably by time sequences."

After he issued his ruling in the case, Ugast also instructed the U.S. attorney's office to begin an investigation into the juror's complaint that she had received threatening telephone calls.

Defense attorney Muse had asked Ugast to declare a mistrial Wednesday because of the unexpected developments in the case this week. Sherman was informed of the court's decision by reporters as he left the hospital yesterday.

The government had contended during the trial that Sherman deliberately performed incomplete abortions, used unsterile instruments and violated medical standards in orde to save time and increase profits at the abortion clinic he once ran in Northwest Washington.

He was charged with causing McDonwell's death as a result of an incomplete abortion and with 25 counts of perjury in connection with what the government contended was his attempt to cover up the circumstances of her death.

The defense argued that McDoowell died as a result of grossly negligent treatment she received at D.C. General and not from Sherman's conduct.