New York ? A massive new federal study documents an unprecedented and dramatic decrease in incidents of serious child abuse, especially sexual abuse. Experts hailed the findings as proof that crackdowns and public awareness campaigns had made headway.

An estimated 553,000 children suffered physical, sexual or emotional abuse in 2005-06, down 26 percent from the estimated 743,200 abuse victims in 1993, the study found.

“It’s the first time since we started collecting data about these things that we’ve seen substantial declines over a long period, and that’s tremendously encouraging,” said professor David Finkelhor of the University of New Hampshire, a leading researcher in the field of child abuse.

“It does suggest that the mobilization around this issue is helping and it’s a problem that is amenable to solutions,” he said.

The findings were contained in the fourth installment of the National Incidence Study of Child Abuse and Neglect, a congressionally mandated study that has been conducted periodically by the Department of Health and Human Services. The previous version was issued in 1996, based on 1993 data.

The new study is based on information from more than 10,700 “sentinels” — such as child welfare workers, police officers, teachers, health care professionals and day care workers — in 122 counties across the country. The detailed data collected from them was then used to make national estimates.

The number of sexually abused children decreased from 217,700 in 1993 to 135,300 in 2005-2006 — a 38 percent drop, the study shows. The number of children who experienced physical abuse fell by 15 percent and the number of emotionally abused children dropped by 27 percent.