John Over, Chief Constable of Gwent, said he was deeply concerned at the inadequacy of the sentence and was alarmed that victims of crime appeared to be treated with less consideration than the criminals.
His comments were reinforced after it emerged that the 15-year- old victim, a former schoolmate of the rapist, who has been expelled, had suffered five months of taunting from other pupils and had to be removed from classes on Friday after the sentencing.
Judge John Prosser, 60, said he thought a prison sentence for the 15-year-old boy, whom he described as 'one of the most popular boys in school', might result in him mixing with people who would teach him 'more bad habits'.
The boy from Cwmbran, Gwent, who dragged the girl off the school's tennis courts and raped her in a nearby wood after demanding a birthday kiss, was also given three years' probation.
The sentence was immediately condemned by the Police Federation and MPs, one of whom, Harry Greenway, Conservative member for Ealing North, demanded that male judges should not in future be allowed to try rape cases.
Marjorie Mowlam, Labour's spokeswoman on citizen's rights, said the ruling was outrageous. 'The judge should not continue in his job as he clearly fails to understand that rape is a crime of violence. Yet again the police have done their job and the legal system has let them down.'
Mr Over echoed her feelings: 'I am also deeply concerned about the fact that the victim of crime is coming very much last. A very great deal is spent on the rehabilitation of offenders and very little on the victims. Decent people are getting heartily sick of the fact that victims are coming last in the queue.'
The girl's father, who cannot be identified, said his daughter had been having a difficult time from other pupils convinced of the boy's innocence.