The D.C. Court of Appeals yesterday overturned the conviction of Morris J. Warren, who was found guilty in 1978 of armed kidnaping, rape, robbery and other charges in cases involving assaults on three women in 1972 and 1973 that were part of a series of attacks known as the "Green Vega" rape cases.

The decision marked the second time that a conviction of Warren has been overturned by the Court of Appeals. Warren, now 33, was convicted in 1973 of four assaults, but the verdict in the fourth case was overturned five years ago.

In yesterday's decision written by Judge Catherine B. Kelly, the court based its reversal of the 1978 conviction on several trial errors. The reversal cited the fact that at his second trial, the D.C. Superior Court jury was read certain incriminating statements that Warren had made to a probation officer. The statements were in a confidential court memorandum prepared for his first trial that should have been revealed only had Warren been convicted, the appeals court said.

Since the original conviction was overturned, Kelly's opinion said, that report should not have been used in his second trial. Such presentence reports are not to be disclosed to the court, Kelly said.

Kelly also wrote that in addition to the presentence report, other inadmissible evidence was presented to the jury that consitituted a "significant part of the government's case" and "substantially influenced the jury's verdict."

Kelly's opinion for the three-judge panel was joined by Judge Julia Cooper Mack. Judge John W. Kern III also concurred in the decision.

Warren, who was given seven concurrent sentences of 15 years to life, is serving a life term in Maryland for first-degree murder in another case, the opinion noted.