A jury of nine women and three men was selected yesterday to sit at the Montgomery County trial of 16-year-old Paul Wersick, the Wheaton youth charged with murdering a Montgomery County tax assessor last July.

The jurors were sequestered after an all-day selection process that began as three new indictments charging Wersick with burglary were handed up by a county grand jury.

Wersick has pleaded not guilty by reason of insanity to the charge that he fatally shot assessor George E. Angerman Jr. during a robbery in an underground garage in Rockville.

One of yesterday's indictments alleged that Wersick burglarized the home of a District police officer last June and stole the officer's .38-caliber service revolver. Police sources alleged that the gun was later used as the murder weapon in the Angerman shooting.

The two other indictments also charged Wersick with burglaries in the Wheaton area. On July 12, two days after the Angerman murder, Wersick allegedly stole a rifle, a box of 300 lead bullets and other items from a home, which he then set on fire, according to the indictment.

On July 14 the youth allegedly stole a clock and a calculator from a third home, and grand jury charged.

Opening statements were scheduled to begin in the murder trial today.