Prisoners sentenced for robbery in South Carolina serve more time behind bars than prisoners sentenced for willful homicide in Arkansas, Illinois, Iowa, Louisiana, Pennsylvania and South Dakota.

In West Virginia, prisoners sentenced for auto theft stay in prison for an average of 41 months -- nearly three times the average for prisoners convicted for forcible rape in that state.

Those findings are part of a National Law Journal study, scheduled for release Monday, saying huge disparities exist from state to state in the amount of time served in prison.

The Journal said the figures were based on Uniform Parole Reports statistics or on Law Enforcement Assistance Administration figures on over 70,000 prisoners paroled in 1976 and 1977 in 37 states, the District of Columbia and in Puerto Rico. Thirteen states either did not keep records on time served or were unwilling to release figures, the Journal said.

The averages for time served ranged from Massachusetts, with all felony sentences averaging 53 months -- mainly because of the state's still sentences for murder -- to South Dakota, with sentences averaging 13 months.

The District of Columbia ranked near the tougher end of the scale, with an average time served of 31 months; Virginia's was 29 months, and Maryland's 22 months.

The study says the average time spent behind bars before parole was 25 months in state prisons and 27 months in federal prisons.

The study also found:

Women spend less time in prison than men, and blacks spend more time behind bars than whites or Hispanics.

Southern states keep inmates in prison longer than other states, and people convicted of crimes against people spend more time behind bars than those convicted of property crimes.

Convicts of negligent manslaughter in the stricter jurisdictions (Utah, Puerto Rico and D.C.) served more than 10 times as long as those in the most lenient: Missouri, Alaska and Nevada, which ranged from eight months to 15 months.

However, a government statistician and the private researcher involved in compiling most of the study said the figures may be misunderstood.

"What it says, and all it says, is that we have 50 different criminal justice systems in this country," said Jim Galvin, director of Uniform Parole Reports, a private, nonprofit criminal justice research agency in San Francisco.

"Everything said is probably true to a greater or lesser extent, but it's probably overexaggerated," said Carol Kalish, a statistician for the federal Bureau of Justice Statistics in Washington.

Galvin emphasized the study does not say that some states are toucher on crime than others, or tougher on some crimes and more lenient on others.

He said the study does not account for different state methods of compiling statistics. In addition, he said that while much of the Law Journal's data came from states, some also came from a different set of federal statistics.

"The standard variation in the cases is very large," Galvin said. "The variation within the categories of crimes is enormous."

Kalish said the study would provide a more accurate picture by using median rather than average length of prison sentences.

A recent report by the Council on State Governments said that in the last four years -- since the National Law Journal's statistics were gathered -- 14 states have changed sentencing laws to abolish parole, and 36 states now have laws with impose mandatory sentences for certrain violent, drug or repeat offenders.