Fewer than 40% of the inmates released from state prisons in 2003 were back behind bars one year after their release, the lowest rate in a quarter of a century, corrections officials announced Monday.

California's two-year return rate, which some experts consider a more useful barometer, also has declined, reaching its lowest point since 1991. That number has been dropping steadily over the last four years. Of the 54,877 inmates who were paroled in 2003, a little more than half — 51.09% — were back in custody after two years of freedom.

The rate at which parolees run afoul of the law again — recidivism — is widely viewed as the most telling measurement of how well programs for inmates and ex-convicts are working.

The reasons for the downward trend are not yet clear. But officials speculated that expanded parolee and prisoner programs, changes in the law and better community services for ex-convicts all played a role.

Acting Corrections Secretary Jeanne Woodford called the new data, calculated by her researchers, "promising."

"While it is still early, this kind of information shows we are heading in the right direction," Woodford said. She added that "every drop in the recidivism rate means fewer victims in our neighborhoods."