A nurse's aide with a ninth grade education, who was trained to take temperatures and measure blood pressure, regularly performed a surgical procedure on patients at the clinic once operated by former Washington abortionist Dr. Robert J. Sherman, a D.C. Superior Court jury was told yesterday.

"Dr. Sherman showed me a couple of times how to do it," Helen Overstreet, 54, testified. The procedure, called cryosurgery, is a process in which an extremely cold probe is used to destroy tissue by freezing.

Overstreet told the jury she performed the surgery three times a week over a three year period, often when Sherman was absent from the clinic.

Earlier in Sherman's trial for second degree murder and perjury, a medical expert for the government testified that it would be a "deviation" from medical standards for anyone other than a physician to conduct cryosurgery.

Overstreet also testified that in January 1976, when she was called to give a statement under oath in connection with a malpractice suit brought against Sherman, she lied at Sherman's request and claimed she had not performed the surgery.

Sherman told her "If I didn't tell the truth he would give me something in my paycheck," Overstreet testified.

On the payday following her false statement in the civil suit, Overstreet, received an extra $50 in her check, she continued.

When she gave that sworn statement, and later when she testified before a District commission that eventually revoked Sherman's license to practice medicine here, Overstreet testified she lied about the cryosurgery and also about the reuse of disposable instruments and syringes at the abortion clinic.

"Dr. Sherman told me to say it," Overstreet responded each time assistant U.S. Attorney Whitney Adams asked her why she had lied.

Overstreet was the fourth government witness called in Sherman's trial, before Judge Fred B. Ugast which recessed for the weekend late yesterday after six days of testimony.

Sherman, 65, is charged with second-degree murder in connection with the death of Rita C. McDowell, a 16-year-old high school student. The government contends it will prove that McDowell died from massive blood poisoning and shock that resulted from an incomplete abortion Sherman deliberately performed on her in his clinic in March 1975.

Principal Assistant U.S. Attorney Carl S. Rauh told the jury of seven women and five men that the government's evidence would show Sherman regularly performed incomplete abortions at the clinic, and that he used unsterile instruments and violated other medical standards in order to cut costs, increase profits and save time.

Sherman is also charged with 17 counts of perjury and nine charges that he induced three employes to lie for him in what the government contends was an effort to cover up the circumstances surrounding McDowell's death. Sherman, who now lives near Richmond, has denied all the charges.

Defense attorney Robert F. Muse told the jury that the evidence would show McDowell's death was the result of grossly negligent treatment she received at D.C. General Hospital, where she died four days after the incomplete abortion.

Moreover, Muse said, defense evidence would show that Sherman used "good medical judgment" when he treated McDowell.

A nurse testified for the government earlier this week that Sherman often performed abortions in his clinic on women past the 12th week of pregnancy - abortions the government contends should have been performed in a hospital. The nurse also described the clinic as dirty and said Sherman reused instruments so often that they became worn and broken.

Alexis Morman, 30, testified that five to 15 abortions were performed daily, and that Sherman increased his fee depending on the length of pregnancy.

Sherman's former office manager, Patricia McCarty, 34, testified that she had lied twice under oath, at Sherman's direction, about procedures at the clinic. She also testified that within a week after McDowell's death, she helped Sherman recreate McDowell's medical chart, which Sherman told her had been lost. She also rewrote appointment books to show far fewer patients and to delete information about fees or length of pregnancy, McCarty testified.

McCarty testified that she frequently saw Overstreet perform cryosurgery, but Overstreet testified yesterday that McCarty was not in Sherman's office when she performed the procedure. Overstreet worked part time for Sherman for five years, and received a take home pay of $80 per week, she testified.

Her voice at times barely audible, Overstreet told the jury that when she performed cryosurgery, a three minute procedure, she inserted the probe into the patient's vaginal canal and then held the instrument on tissue that she saw - by its colour - was infected and needed treatment.

Contrary to earlier testimony, Overstreet told the jury that she thought the clinic was "clean." She never saw Sherman discuss fees with patients in the examination room, she said, but she saw him give patients money for prescriptions and transportation from his office.