A D.C. Superior Court jury yesterday convicted a 27-year-old Washington man of second-degree murder in connection with the shooting death of an off-duty police detective last December.

Sixteen days before the murder, the same defendant, Charles Alexander Phillips, had pleaded guilty to murder and assault in connection with the stabbing of another man. Both murders took place in the apartment of Phillips' former girlfriend. Phillips was free on bond at the time of the second murder.

The jury of three men and nine women returned their verdict yesterday to Judge John R. Hess after deliberating four hours. The jury also found Phillips quilty of unlawful entry and carrying a pistol without a license but acquitted Phillips on a charge of armed robbery.

According to the prosecution Phillips went to the apartment of Carolyn Radford at 3417 Minnesota Ave. SE early in the morning of Dec. 22, 1977, broke in a back door and confronted Radford and Det. Michael K. Riley in the bedroom.

Phillips ordered Riley out of the apartment, according to Assistant U.S. Attorney Martin J. Linsky. Riley, who had his service revolver in his pants pocket, struggled with Phillips as he tried to leave the room and was shot, Linsky said. Radford had rushed to a telephone in another room and did not witness the shooting, Linsky said.

Phillips, who testified in his own defense, told the jury that Radford, his former girlfriend, had agreed to allow him to come to the apartment that evening to pick up some personal papers. Phillips testified that he kicked in the door after it appeared that Radford was not at home. Phillips admitted he told Riley to leave, but he testified Riley "started giving orders," reached for the pistol and pointed it at him.

"I reached for the pistol and we struggled over it. We fell to the floor and started wrestling. Then the pistol went off," Phillips testified. Riley was an eight-year veteran of the police force.

In January, Phillips, who lived at 1617. F St. NE., was sentenced in Superior Court to a term of 15 years to life in prison tor the murder of Napoleon B. Wilcox, 43, and to a consecutice term of 40 months to 10 years in prison in connection with an assault on Carolyn Radford.