The Montgomery County state's attorney's office announced yesterday that it has dropped one of the five remaining rape charges against Timothy Joseph Buzbee, the prime suspect in what have become known as the Aspen Hill rapes.

Assistant State's Attorney Barry Hamilton said the evidence was insufficient to try Buzbee on charges of rape in an incident that occurred in January 1982. It was the second time the prosecution has dropped a case against Buzbee, who was charged last November with five rapes and one attempted rape.

Buzbee has pleaded not guilty to all of the charges.

Hamilton made his announcement before Circuit Court Judge John J. Mitchell, who was presiding yesterday at the selection of a jury in another of the trials involving Buzbee. Hamilton added that dropping of the charge in the case did not mean that prosecutors feel Buzbee is innocent.

Buzbee's attorney, Reginald W. Bours III, immediately argued that it was improper for the prosecutor to make comments concerning Buzbee's guilt when the charge had been dropped for lack of evidence.

Mitchell completed jury selection quickly for a trial in which Buzbee is charged with a kidnaping and rape in July 1981.

Mitchell denied a defense motion that the jury be sequestered to shield it from publicity about the case. However, Mitchell instructed the jurors that they are to avoid all news programs on radio and television during the trial.