Initiating a sexual relationship with a minor generally guarantees a jail term; however, a Chester County judge departed from the norm yesterday, calling the case one of the most unusual he had ever seen.

President Judge Howard F. Riley Jr. said he believed incarceration would put Matthew D. Giannascoli at risk and would not serve society. As a result, he sentenced the 21-year-old Bryn Mawr man to 10 years' probation, the first year of which must be spent on electronic home-monitoring.

Riley said Giannascoli must continue to receive psychological treatment, complete the sex offenders' program, and avoid any contact with the victim or her family.

The judge said psychologists for both the defense and the prosecution agreed that Giannascoli, diagnosed with various developmental disorders, functions "emotionally as a 14- or 15-year-old."

In addition, the experts said negative personality changes have been reported as side effects of the drug Straterra, which Giannascoli began taking several days before his visits with a 14-year-old girl he met in an Internet chat room. Straterra is used to treat attention disorders.

"I cannot rule out the possibility that the medication may have triggered behaviors which were uncharacteristic for the defendant," said Bruce Mapes, a forensic psychologist who concluded that Giannascoli was not a sexually violent predator.

In another courtroom yesterday, a New Jersey man received a more typical sentence for similar charges: 30 to 72 months in prison for attempted involuntary deviate sexual intercourse and sexual assault.

Chester County Court Judge Juan R. Sanchez accepted the terms of a plea agreement that also called for Mont Edward Shatley Jr., 34, of Paulsboro, to spend five years on probation after the jail term.

Shatley, who presented no history of psychological problems, entered a guilty plea in September, admitting that he picked up a 15-year-old girl on Aug. 19, 1999, in Parkesburg, forced her to have sex with him, and threatened her if she told anyone. She did not report the attack for more than two years.

Giannascoli, who pleaded guilty in September to attempted involuntary deviate sexual intercourse, indecent assault, and corruption of minors, admitted that he began a two-week online correspondence with the victim, who was in the eighth grade.

He said the girl gave him directions to her house so they could meet when her parents were away. The parents came home early on March 28, his third visit, and found Giannascoli undressed in their daughter's room.

Assistant District Attorney Kimberly A. Callahan said that factoring in Giannascoli's limitations did not change the severe impact on the victim and her family. She said a sentence in the standard range - 36 to 54 months - would be appropriate.

Giannascoli knew his behavior was wrong, Callahan argued. Otherwise, he would not have entered the girl's home through a bedroom window or lied about his age, Callahan said.

The girl's mother said the family had added an alarm system and a dog in an effort to recover some sense of security, but her daughter's nightmares continue.

Before this incident, the family had a "false sense of security," the mother said, adding that Internet access can be the equivalent of "throwing the front door open."

Defense attorney Robert J. Donatoni said Giannascoli's emotional immaturity and small stature would make a jail term "barbaric."

Gerald Cooke, a forensic psychologist hired by the defense, said he believed Giannascoli would be a suicide risk in prison, where he would "have to be kept in protective custody." Also, he would not get the help he needs since "security is more important than treatment" in prison, Cooke said.

Addressing the court in his own behalf, Giannascoli said, "If you put me in jail ... you would do my family and me a bad thing. What my doctor said about committing suicide, I would do it if I was in there."