The study focused on children younger than 1, and found nearly a third were one week old or younger when the abuse or neglect occurred.
Most of these cases involved neglect, and may in part reflect families without health insurance that are not getting adequate care for their children, said David Finkelhor, who is familiar with the data but was not involved in the study. Finkelhor directs the Crimes against Children Research Center at the University of New Hampshire.
"It's not primarily kids being hit, but parents showing signs of not being able to really care for their kids," he said.
The researchers counted more than 91,000 infant victims of abuse and neglect in the period Oct. 1, 2005 to Sept. 30, 2006.
The information came from a national database of cases verified by protective services agencies in 45 states, the District of Columbia and Puerto Rico.
Other studies have looked at national child abuse and neglect cases, but this is believed to be the first to focus on infants, said study co-author Rebecca Leeb, of the Centers for Disease Control and Prevention.
The results mirror what a study in Canada found, Leeb said.
The 91,000 infants were age 1 year or younger. About 30,000 of those cases were newborns aged one week or younger.
"It is a particularly vulnerable group," said Leeb, a CDC epidemiologist.
"We were struck by the fact there was a clustering of maltreatment with the very, very early age group."
Only about 13 percent of the newborn cases were counted as physical abuse, meaning the large majority involved neglect. Federal officials define neglect as a failure to meet a child's basic needs, including housing, clothing, feeding and access to medical care.
The counted cases did not include new parents stumbling their way through breast-feeding or making other rookie mistakes.
"Things like abandonment and newborn drug addiction would qualify as neglect, not things like parents learning how to be parents," Leeb said.
Medical professionals identified about 65 percent of the maltreated newborns to protective services staff. The others came from law enforcement, relatives, friends, neighbors and from protective services staff.
Finkelhor has written reports from the same database the CDC researchers used. He said the neglect cases include situations in which medical professionals conclude that a child got sick or didn't correctly develop because parents didn't get recommended medical care. Those cases were not necessarily life-threatening, he added.