In an unusual move, D.C. Superior Court Judge Fred B. Ugast decided yesterday to postpone -- after the jury's virdict -- his ruling on a defense request that former Washington abortionist Dr. Robert J. Sherman be acquitted by the court of the second degree murder of 16-year-old Rita McDowell.

Ugast's decision followed defense arguments that the prosecution evidence failed to prove that Sherman maliciously disregarded the life and safety of his patients -- an essential element of the second degree murder charge.

Defense attorneys Constance O'Bryant and Robert F. Muse said they contended that based on the evidence introduced during Sherman's six-week trial, the jury could not find Sherman guilty of the murder beyond a reasonable doubt -- the legal standard in criminal cases.

The emotional nature of the case, however, might lead to such a verdict, the defense attorneys said in asking Ugast to acquit Sherman of the murder charge himself.

Three weeks ago at the close of the main part of the government's case, Ugast denied a defense motion for acquittal on the murder charge. Yesterday, Principal Assistant U.S. Attorney Carl S. Rauh renewed his arguments that the evidence showed Sherman routinely used unsterile instruments, performed incomplete abortions and violated additional fundamental medical standards in order to increase profits at his clinic.

Following argument from both sides, Ugast said he would reserve judgment on the murder count until after he heard closing arguments, scheduled for Monday, and the jury had reached a verdict in the case. Expressing concern over the seriousness of the case, Ugast told the attorneys it was the first time he had made such a decision -- permitted under Superior Court rules -- since he came to the bench five years ago.

At the hearing yesterday, Ugast denied defense motions for a judgment of acquittal on 25 perjury counts against Sherman. Those charges relate to what the government contends was an attempt by Sherman to cover up the circumstances surrounding Rita McDowell's death. McDowell died in the intensive care unit of D.C. General Hospital on March 8, 1975, four days after she went to Sherman's clinic for an abortion.