Paul Wersick, the 15-year-old Wheaton youth accused of slaying a Montgomery County tax assessor last week, was indicted yesterday on charges of murder, armed robbery and illegal use of handgun.

According to the indictment, Wersick allegedly stole $26 in cash, a black leather wallet, and a Timex digital watch, worth a total of $72, from George E. Angerman, 36, who had been a county residential tax assessor for the past seven years.

Angerman was found dead July 11 in the driver's seat of his car in the parking garage of the Unibank office building in Rockville where he worked. He had been gagged with a red handkerchief and shot once in the left of the head, police said. Some rope was attached to his left wrist, leading police to believe that he had been bound before the shooting.

Police still are searching for the handgun believed used in the slaying. Informed sources said a gun holster was found in Wersick's bedroom on the day of his arrest and has been traced to a D.C. police officer whose home in Wheaton was burglarized June 20. According to the police report on the burglary, a handgun and a calculator were taken from the officer's house.

A field near Wersick's home at 13057 Viers Mill Rd. is being searched for a weapon.

Wersick, charged as an adult, is being held without bond in the County Detention Center pending a psychiatric evaluation to determine whether he is competent to stand trial.

In an unusual move, Wersick's attorney, Joseph Quirk, obtained an injunction from the County Circuit Court Wednesday Night stopping discussion of the murder case by all police, court, and school personnel as well as members of the Maryland Department of Juvenile Services.

In December 1975, the county Juvenile Court found Wersick "responsible for the shooting death of one of his playmates, 11-year-old Cynthia Martin. The current injunction, signed by Circuit Court Judge H. Ralph Miller also prevents those familiar with the case from discussing the Martin shooting. The injunction expires Monday.

Police have said they first encountered Wersick last Saturday afternoon as they searched a wooded area near the apartment complex where Wersick lived with his mother, and where a county employe had earlier found Angerman's wallet.

Wersick was taking photographs of animals in the wooded area, and talked with police briefly about how the movie "Star Wars," and its villain, Darth Vader, according to informed sources.

Afterward, police checked the fingerprints of Wersick and other youths who were known to spend time in the wooded are against those found at the shooting scene.

Described by neighboors and school officials as a socially withdrawn "small and quite boy," Wersick had been receiving psychiatric treatment. He had attended Mark Twain School in Rockville, which has a special program for students with emotional problems. Wersick had been living with his mother, who is a clerical worker for the Montgomery County Council.