Hard-core juvenile deliquents commit fewer crimes after confinement, whether in a group home or a traditional reformatory, and the tougher the restrictions on their behavior, the greater the decrease in crime, a newly released study has found.

The study, which challenges popular theory that institutionalization does not work for serious juvenile offenders, has caused a furor among some juvenile justice specialist who are critical of the study's methods and fear it will be used to put more delinquents in jail.

"If it's accurate that incarceration has this kind of impact, then that could have major policy implications," said Andrew C. Gordon, an associate professor at the Center for Urban Affairs at Northwestern University who reviewed the study's early findings and disagreed with them.

"It's certainly the case that it is not a conclusion that one wants to implement lightly," Gordon said.

The study, conducted by the American Institutes for Research, is based on a sample of about 600 chronic juvenile offenders in the Chicago area between October 1974 and July 1976. The youths were either confined to one of the state's seven traditional juvenile institutions or placed in one of five programs designed as alternatives to incarceration for serious juvenile offenders.

The study compared the youths' annual arrest rates before and after confinement. Chronic deliquents who were committed to the traditional institutions showed at 68 percent drop in arrest rates, and those placed in the five types of treatment programs showed an overall 59 percent decrease.

". . . [At] home services, group homes, out-of-town camps, traditional institutions -- all produced a major drop" in the crime rate, the study said.

But the arrest rates dropped more as the programs got more restrictive and as the youth was taken farther from his or her normal environment, according to Charles A. Murray, chief scientist at the American Institutes' Washington office and a co-author of the study.

The researchers speculated that part of the success of the less restrictive programs could be attributed to the threat that the youth would be sent to a traditional institution if he or she didn't change his ways, Murray said.

The youths in those programs knew that their status as offenders had changed -- their penalty had gone beyond probation or supervision -- and they knew the "criminal justice system was no longer bluffing."

The study was funded with $286,000 from the Illinois Law Enforcement Commission and the federal Law Enforcement Assistance Administration.

The study called "Beyond probation," which is to be released in book form later this month, clearly reveals the disagreements that have preceded its publication. The text is written in a highly deefensive tone and the researchers carefully address each technical argument that critics have used to dispute their findings.

"Many social work and treatment professionals have always said institutions are inhumane settings," said Betsy Reveal, the executive director of the District of Columbia's Office of Criminal Justice Plans and Analysis.

Objections to the institute's findings, Reveal said, are "coming from treatment professionals being unwilling or unable to accept empirical evidence restrictive alternatives."