A D.C. Superior Court jury yesterday convicted a 30-year-old Washington laborer of first-degree murder and rape in the June 1981 slaying of a Georgetown University student in a wooded area of Rock Creek Park under the Whitehurst Freeway.

The jury found Donald E. Gates, who already is serving a sentence in D.C. Jail for attempting to rob another woman in the same location, guilty of shooting 21-year-old Catherine Theresa Schilling, of the 3000 block of N Street NW.

Schilling, who worked as a para legal aide in a law firm in the Watergate Office Building, often took a shortcut home in the evening by walking along a path in Rock Creek Park. She took that darkened path home the night she was killed.

Coworkers began searching for her the next day after she failed to report to her job, and they found her body on the east bank of Rock Creek, about 100 feet from the parkway. She had been sexually assaulted and shot once in the face and four times in the back of the head.

A few days after the shooting, police received a tip from an informant who said Gates had told him he started to rob a woman in the park and that he had raped and killed her.

Investigators then discovered that Gates had been arrested 19 days earlier for attempted robbery of another woman in virtually the same location. Gates, who was free on bond pending arraignment in that case when Schilling was attacked, later pleaded guilty to the first incident and is serving a 10-to-30 month sentence on that case.

Judge Fred B. Ugast yesterday ordered Gates to appear for sentencing Oct. 28.

Gates faces a mandatory minimum sentence of 20 years and a maximum sentence of life in prison for the murder, as well as a minimum three and one-third years for carrying a pistol.

Homicide detectives said yesterday they were still investigating the murder two weeks ago of 38-year-old Gail Ornstein, a jogger who was found strangled, beaten and sexually assaulted by the side of a running trail in Rock Creek Park near the Connecticut Avenue bridge. No arrest has been made in that case.