About four-fifths of the persons placed in state prisons during 1979 were repeat offenders, and 40 percent were on parole or probation when they went back behind bars, the Bureau of Justice Statistics reported in the first nationwide study of its kind.

Nearly two-thirds of the group had been incarcerated previously as adults, juveniles or both, according to the study released yesterday. Of these, nearly half (46 percent) would still have been incarcerated for earlier crimes if they had served the maximum term of previous sentences. The study calls them "avertable recidivists."

Of those who had never been in prison, 60 percent had at least one previous conviction for a criminal offense.

"These findings raise serious questions about the impact of probation and parole decisions on public safety, and create a challenge for those who set sentences and shape sentencing policy," bureau director Steven R. Schlesinger said in a statement accompanying the report. The bureau is a Justice Department agency.

The report is based on interviews with a nationwide sample of 5,357 inmates, representing 153,000 men admitted to state prisons in 1979. Previous studies of repeat offenders in prison have focused on individual communities and relied primarily on police records rather than on interviews with offenders, officials said.

Among other findings:

* Half the inmates released from state prisons return within 20 years, with most within the first to third year.

* Offenders committing robberies, burglaries or auto thefts were returning more rapidly than those committing violent crimes such as murder, rape and assault.

* The younger the prisoners were at release, the higher the rate of those returning within the first year. Of those between ages 18 and 24 upon release, 22 percent returned to prison within a year. The percentage of returnees dropped sharply for those older than that group.

* Half of the repeat offenders had four or more prior sentences of probation, jail or prison. About one in nine had more than 10 prior convictions.

The report is not an attack on parole and probation, bureau officials said.

"The study underlines the logic of the justice system," said Lawrence Greenfeld, director of correctional statistics. "To get to prison as a first timer, you have to commit a very serious crime. Conversely, to get to prison with a less serious offense, you are likely to be a recidivist."

The findings have implications for early-release programs around the country, he said. "It may be that the people being released [often those classified as nonviolent] are those most likely to be coming right back in again . . . . We need to know more about behavior and what characteristics are linked to early failure."

An update of a second study by 12 prominent university experts found that violence in America has risen since the group's 1969 study, Reuter reported.

"The federal government's policy of deterrence during the 1970s, through more efficient police hardware and more efficient police, courts and prisons, simply did not work," said the report by a White House commission chaired by Milton Eisenhower.

["The level of crime in the United States remains astronomical when compared with that of other industrialized democracies," it said.]