Officials at Children's Hospital in Washington are investigating a sudden, unexplained increase in the number of children aged three years and younger who have died recently as the suspected victims of child abuse.

Four infants -- three from the Maryland and Virginia suburbs -- died as a result of injuries allegedly inflicted by their parents or other adults during a six-week period in November and December, according to hospitals records.

Alarmed by the sharp increase, hospital officials say no more than two such deaths had been reported annually since 1974.

The increase brought the total numberof such deaths to six in 1979.

"It's certainly a lot more homicides relating to child abuse than we usually see," said Dr. Daniel Ochsenschlager, head of the hospital's emergency room. "People should be aware that children are being beaten up."

Officials said there was a dramatic increase in the overall number of suspected child abuse victims brought to Children's Hospital in November, many of them from the suburbs.

The four infant deaths have been investigated by local police departments. Two of the victims were from Montgomery County, one was from Fairfax County; the other from the District.

Montgomery County police detective Charles Peters, who investigated the death of a 15-month-old girl as a result of a skull fracture, said "the deaths sound like a freaky coincidence."

Police and local hospital officials say they usually refer their more serious cases to Children's Hospital, 111 Michigan Ave. NW, because of the facility's national reputation.

But Children's Hospital officials say there has been no policy change that would have resulted in a sudden increase in referrals. And although officials say they see a slight increase in child abuse cases during the Christmas holiday period, they are baffled by the recent fatalities.

According to a study conducted by the hospital child abuse division at the request of Dr. Ochsenschlager, three of the four victims were female infants from the suburbs. All three were treated at local hospitals before being referred to Children's Hospital. All three died after two to four days in the intensive care ward, the study said.

The fourth victim was a baby boy who had ben identified previously by District police as a suspected abuse case, sources close to the investigation said.

The study, conducted by the hospital's Child Protection Center, identified the four victims as:

A 2-year-old girl from Montgomery County who died at Children's Hospital in early November as a result of a skull injury. Police investigators said the pathologist report concluded that the skull fracture was allegedly caused by a blow inflicted by another person. Although police said a criminal indictment was recommended in the case, a grand jury declined to press charges.

A 13-month-old girl from Fairfax died at the hospital later that month as a result of brain and eye injuries. Fairfax police say the case is still under investigation.

A 15-month-old girl from Montgomery County who died in late November as a result of a skull fracture. According to police, the case is still under investigation.

A 3-year-old boy from the District who died in December from head injuries. Although police had received reports several months earlier that the child was a suspected abuse case, they were unable to obtain enough information to press charges, sources said. The fatality is currently being investigated by District police.

Police and hospital officials said that several cases seemed unusual because there was no history of child abuse in the family.They were also surprised at the large percentages of cases from the suburbs.

"It doesn't appear to be a city thing any longer," said one official. "Is there a demographic change happening? A lot of the kids we were seeing were from the District. But we must keep in mind that one month's figures don't make a trend."

Children's Hospital officials said they had seen 18 abuse cases overall during the first week of this year. Cases of suspected child abuse brought to the hospital have doubled in the last four years. In November of 1978, for example, there were 28 victims of suspected abuse treated at the hospital's special unit. In November 1979, that figure had jumped to 58.

The hospital study also showed that the total number of allegedy abused infants during November -- including those who eventually died -- was approximately four times the figure normally recorded at the hospital.

All but one were female, the study said, and most were from the suburbs.

The youngest was a 6-week-old girl from Prince George's County who was taken to Children's Hospital in November with head injuries and human bites on her body, a hospital official said.