Deep in the basement of the Los Angeles County coroner's office, two Los Angeles Police Department detectives huddle over a tiny body. It is almost lost on the autopsy gurney. It is a baby boy.

Christopher's mother said he died sleeping in his crib, apparently of sudden infant death syndrome. But the prognosis changes as the coroner cuts the little boy's head to reveal the skull. The flesh is red, bruised. There are two half-inch fractures. Baby Christopher, it seems, may not have died so innocently.

"He was just 1 month old," LAPD detective Carmen Ibarra says quietly.

It is a scene Ibarra--and police around the country--increasingly face as the number of children killed by their parents and caretakers continues a grim and steady climb. In 1991, Los Angeles County saw such homicides increase by a third. Nationwide, the government says four children are killed by their parents or guardians each day--a 54% jump in the last six years to 1,383 fatalities in 1991.

Statistics kept by the Orange County Sheriff's Department do not have breakdowns for infants but only list homicides of children under 12. In 1991, Lt. Bob Rivas said, there were eight in that age group killed, 14 last year.

Child advocacy groups note that many children's deaths are not investigated and estimate that more than three times that number are shaken, suffocated or bludgeoned to death each year by the very people meant to protect them. More than half of these children die before their first birthday.

Authorities say the killings are fueled by mounting stresses on dysfunctional families and government's failure to protect its most vulnerable.

A national survey by the National Committee for Prevention of Child Abuse found that more than 41% of child abuse deaths occur after intervention by child protective service agencies. One 10-month-old Los Angeles boy was beaten to death after 52 contacts with child protective, law enforcement and other agencies, none of which knew about reports made to the others.

Child protective agencies fail to investigate one in five calls reporting abuse. Even in cases where child abuse is substantiated, 37% of children get no services, up from 22% in 1990, a survey by the child abuse advocacy group found.