A fisherman who pleaded guilty to killing his 3-month old nephew when he tossed the baby into a ceiling light fixture during a drug-induced hallucination was sentenced yesterday to 20 years in prison for second degree murder.

Fairfax Circuit Court Judge Barnard F. Jennings imposed the sentence, the maximum allowed for the offense, on Thomas S. Jenkins, 23, a Newport News, Va., commercial scallop fisherman who had been visiting his sister's family at their Annandale home at the time.

"This is just one of the many examples we've seen of the effects of using PCP phencyclidine ," Jennings told a pale, shaken Jenkins at the sentencing hearing. "I can't help but believe you were aware of some of the potential consequences."

Jenkins' mother and other family members burst into loud sobs after Jennings imposed the sentence.

One of Jenkins' sisters testified yesterday that Jenkins had been given the PCP by the baby's parents who, along with other friends, had encouraged him to use the drug several times before the incident in which the baby was killed.

"What they the family did was a crime, also," Jennings said yesterday. "Regardless of whether they supplied the PCP , doesn't justify what you did."

Defense attorney Warren W. McLain had asked the judge for a lesser sentence, saying PCP was "primarily responsible for the crime that took place here." McLain said Jenkins didn't realize he had killed the baby until several days afterward.

Commonwealth's Attorney Robert F. Horan Jr. lashed out at McLain's argument, declaring that Jenkins was saying: " 'Please excuse my crime because I was involved in another felony using PCP at the time I did it.' "

Jenkins, in a trembling voice, told the judge, "I'm sorry for what happened. I'm not trying to make excuses for myself. I hope you'll let me go back to work and to finish my education."

During an earlier court hearing, police investigators testified that Jenkins had been smoking PCP and reading the Bible at his sister's home last Nov. 20 before he walked into the bedroom where the baby, Jonathan O. Dyer, was sleeping. Police said Jenkins picked up the sleeping baby from his crib and tossed it into the air. The infant's head hit a light fixture, fracturing his skull.

"I killed the devil," Jenkins told the parents, Diane and Bruce Dyer, after the incident, according to court records. Police said Jenkins apparently was hallucinating after using PCP.

McLain told the sobbing family members after the sentencing that Jenkins could be eligible for parole in slightly less than four years.