The mother of a 16-year-old high school student who died four days after she was treated by former Washington abortionist Dr. Robert J. Sherman collapsed into tears during her testimony yesterday, interrupting the eighth and most dramatic day in Sherman's trial on charges of second-degree murder.

Grim-faced jurors, some of whom seemed to be fighting back tears, were led from the courtroom for a recess called by D.C. Superior Court Judge Fred B. Ugast, who then immediately left the judge's bench.

Sherman, 65, who had been taking notes on long sheets of yellow paper during Lupe M. McDowell's testimony, was expressionless. He remained seated with his defense lawyers while McDowell was led from the courtroom.

Fifteen minutes later, McDowell returned to the witness stand and in a soft, deep voice recalled the circumstances that ended with the death of her daughter, Rita, in the early morning hours of March 8, 1975.

"Rita was in great pain, I could see it in her face," McDowell testified about her daughter's condition after she was treated at Sherman's clinic.

"She said 'Momma, I feel like I've been stuck with 16 needles," McDowell testified. "She could hardly walk."

They went to the clinic together, McDowell said, and when they left she was given a prescription for Rita, an appointment for another visit with Sherman two days later, and instructions from a woman at the clinic that Rita would probably experience an abortion sometime that evening.

The next day, McDowell testified, she called Sherman's office because she wanted to tell him Rita had a 102-degree temperature and that "the baby had not come down." Four hours later, a woman in Sherman's office telephoned McDowell and told her to bring Rita to the office on Friday March 7, a day later than her scheduled appointment, McDowell testified.

Early that Friday morning, McDowell said she was suddenly awakened. "Rita said 'Mama!' So I jumped up and ran to her room," McDowell testified, her voice breaking. Rita said she thought the abortion was about to occur, McDowell testified.

"All of a sudden she slumped back . . . I held out my arms and she fell into my arms and was screaming," McDowell testified. She began to sob and Ugast called the recess.

Rita McDowell was rushed to D.C. General Hospital in an ambulance, her mother later testified. A few minutes after 2 a.m. on Saturday, March 8, 1975, Rita McDowell died.

At one point, Mc Dowell told the jury that Rita's son, Tony, now 5 years old, was present in the courtroom. The child, dressed in a burgundy and gold Redskins jacket, lay asleep in the arms of a family friend while his grandmother testified.

Government witnesses had described, often in graphic detail, abortion procedures at Sherman's clinic, once located at 1835 I St. NW. The prosecution charges that Sherman deliberately performed incomplete abortions, used unsterile instruments and allowed unqualified personnel to perform surgical procedures so that he could save money and increase profits at the clinic.

Sherman's license to practice medicine in Washington was revoked in September 1977 after an extensive investigation into the death of Rita McDowell. Sherman now lives near Richmond.

The trial, which began Oct. 27, has been marked by emotional, sometimes dramatic testimony. In one unusual development Monday, a woman juror was excused from the case after she disclosed that a witness who was about to begin her testimony had dated a close relative of the juror's, had becme pregnant and had had an abortion.

The trial resumed yesterday with sensitive testimony from a young woman who said that at the age of 15 she went to Sherman for an abortion with $300 that her boyfriend had taken from his credit union. The woman said she was four months pregnant at the time.

The woman's sister later testified that Sherman told her that in order to complete the abortion the woman would have to pay an additional $300 to $500 for a second procedure.

The sister, who lives in Delaware, testified that when she told Sherman she could not afford the additional payment, he gave her a green plastic bag and told her it was "possible on the way home (that the woman) would have an abortion."

In a bitter voice, the sister testified that Sherman said "it might be a good idea" to dispose of any products of the abortion in the Chesapeake Bay as they made their way home over the Bay Bridge.

The abortion did not occur, the sister testified. The next day, the young woman was taken to a local hospital where that night she aborted.