A 17-year-old Alexandria youth was sentenced to 43 1/2 years in prison yesterday by a Virginia circuit court judge for the brutal assault and robbery of a woman in her apartment last January.

An Alexandria jury convicted Douglas Newton on June 3 of assault, statutory burglary, robbery and grand larceny charges growing out of the incident and recommended a prison term for Newton of 53 1/2 years. Judge Wiley R. Wright Jr. yesterday cut 10 years from that recommendation, ordering that Newton remain on probation for 10 years after his prison term and receive psychiatric counseling during that period.

Newton will be eligible for parole in about 10 years, prosecutors said.

Deputy Alexandria prosecutor Richard Mendelson said yesterday he regarded the sentence as "not that stiff" considering the event. "This was a horrible crime," Mendelson said.

Both Newton, who was tried as an adult, and a 14-year-old accomplice were convicted in connection with the Jan. 8 incident, which occurred in the woman's residence at the Hamlet Apartments on Van Dorn Street near the Landmark shopping center.

The juvenile was freed about two weeks ago after spending nearly three months in a correctional facility.

Newton's defense lawyer, Gerald D. Lee, had argued that his client should receive a shortened sentence since the juvenile already has been released. But prosecutors opposed the move, noting that Newton already had a juvenile criminal record.

According to trial testimony, Newton and his compansion gained entry to the woman's apartment by first saying they wanted information about a neighbor and then saying they wanted to use the restroom. Once inside, they attacked the woman, stabbing her repeatedly with a knife and a scissors and beating her with a rolling pin. The woman's hair was shaved, her money and car were taken and she was left for dead.

The woman, now recovered, testified at the two-day trial and identified Newton as her assailant.