Three decades after the notoriously harsh Rockefeller drug laws were enacted, the state’s prison sentences for narcotics offenders were lessened yesterday when Governor Pataki signed reform legislation.

The new law reduces by nearly 50% the minimum sentences for first-time, nonviolent drug offenders. The old laws, which had minimum sentences of 15 to 20 years to life, are replaced by sentences of eight to 20 years. In addition, the threshold weights on drug-possession crimes were doubled.

Mr. Pataki said the Rockefeller drug laws, enacted in 1973, were written “at a time when we didn’t know as much about drug addiction as we do today.”

“Thirty years later,” the governor said, “we all know they didn’t work.”

Assembly Member Joseph Lentol, a Democrat of Brooklyn, said he voted to ease the Rockefeller drug laws because when he was a prosecutor, he “saw firsthand the devastation of drugs but at the same time saw how drug mules and others were targeted, not the kingpins.” Under the new law, judges will have the opportunity to rehear their cases to adjust sentences if they see fit – a move that has “added a measure of fairness to the scales of justice,” Assembly Speaker Sheldon Silver, Democrat of Manhattan, said.

The drug-law reform reflects a shift in attitudes from 30 years ago, with a greater emphasis today on treatment as opposed to incarceration.

The chairman of the Assembly Corrections Committee, Jeffrion Aubry, Democrat of Queens, said the handling of drug offenders is a criminal-justice issue that “in the long run, has medical and social answers.”

“Lives that have been wasted and lost to substance abuse are one of the saddest parts of our history,” Mr. Silver said. But first-time, nonviolent offenders should be allowed to seek treatment, to “halt their slide into the abyss,” the speaker said. The president of the New York State Bar Association, Kenneth Standard, said that although “substantial progress” was made yesterday, he wants judges to be given more discretion in imposing sentences and more accountability, and he wants to see more treatment programs for offenders.

The question of how to pay for these changes persists, he said, but in the long run it is “cheaper to treat people than punish people.”

Another aspect of the new law is “earned merit time” – otherwise known as “time off for good behavior,” which in the past reduced an inmate’s sentence by one-sixth. Under the new law, prisoners are entitled to earn an additional one-sixth off their total time behind bars by earning their general equivalency diploma or participating in a facility-based treatment program. The goal is to help them be reintroduced into society.

Along with the chairman of the Hip-Hop Summit Action Network, Russell Simmons, the actor Charles Grodin was among the activists present at the signing who have been pushing for the reforms. He decided to take up the crusade after hearing the story of Elaine Bartlett, a mother of four with no prior record who served 16 years in prison for selling cocaine before being granted clemency. She is the subject of a book, “Life on the Outside: The Prison Odyssey of Elaine Bartlett,” by Jennifer Gonnerman. Bartlett’s story also influenced several lawmakers who pushed for change.

Mr. Silver said that before joining the Assembly, he spent three years as a narcotics prosecutor. “I saw the Elaines going into the system,” he said, “and I understand what bringing some discretion to the judges would mean to the entire system.”