A 19-year-old youth was found guilty of second-degree murder and a 17-year-old was found guilty of attempted robbery yesterday in connection with the fatal sidewalk assault in January, 1976, on Gladys H. Werlich, Washington society matron.

A D.C. Superior Court jury returned the verdicts after deliberating for less than an hour. Leroy Parker, who was convicted of murder, and Rickey R. Weaver, 17, remained expressionless as the jury's findings were announced.

Both had been charged with felony murder. This is murder committed in carries the same penalty as first degree murder. In this case, the other crime was an attempt to rob Mrs. Werlich of her pocketbook on Corcoran Street NW, about 200 feet from her home at 1625 16th St. NW.

The attack occured on the afternoon of Jan. 13, 1976. Mrs. Werlich was knocked down and struck her head on the pavement. She died of head injuries six days later at George Washington University Hospital.

Dr. Michael W. Dennis, a neurosurgeon at the hospital, testified during the three-day trial that Mrs. Werlich had been kept alive for the six days by mechanical devices. He said these devices were withdrawn after consultation with Mrs. Werlich's son, Robert, when the outlook for recovery became hopeless.

Charles F. Stowe III, Parker's attorney, asked Judge Nicholas S. Nunzio to instruct the jury to consider the following question: Did the withdrawal of the life-supporting equipment deprive Mrs. Werlich of any chance of surviving her assault for a year and a day? Or would she have died within that time anyway?

Stowe asked that this question go to the jury because of an ancient common law rule that holds that the perpetrator of injuries on another person is not guilty of murder if the victim lives for a year and a day after the injuries are suffered. Nunzio denied the request. He said Stowe had failed to develop a proper evidentiary base for such an instruction to the jury during his cross-examination of Dr. Dennis and other witnesses.

The other witnesses included Frank Mason Jr., who pleaded guilty to felony murder in the case last September, and a 13-year-old youth who was found by a juvenile judge to have been "involved" in felony murder in Mrs. Werlich's death. Juveniles who commit crimes are said to be "involved" rather than "guilty."

Mason, 18, testified that he, Parker, Weaver, and the 13-year-old had followed Mrs. Werlich down Corcoran Street with the intention of snatching her purse. He said Parker reached for the purse, but that Mrs. Werlich managed to hang on to it.

Mason said that he himself then struck the woman between the shoulders with his elbow, knocking her down. He said Weaver and the 13-year-old stood at the entrance of an alley during the attack and that all four youths then fled.

Under the "aiding and abetting" theory of law, all persons engaged in a crime are equally guilty of any crime committed by any member of the group. It was because of this theory that all four were charged with felony murder.

The lesser count of second degree murder carries a miximum of 15 years to life in prison for adults. Attempted robbery carries a penalty of one to three years in prison. But all four could be sentenced under the Youth Corrections Act, which generally limits sentences to six years.