On the heels of a federal decision to retroactively reduce prison sentences for crack cocaine offenders, judges in the city have granted motions to release defendants from federal prisons, defense lawyers and court officials said.

Three crack cocaine offenders had their sentences reduced in federal court in Manhattan and will be released from prison within the next 10 days as a result of the March 3 retroactive date, set by the U.S. Sentencing Commission.

The shortening of sentences for crack cocaine offenders, a decision lambasted by some Justice Department and elected officials who warned that releasing the offenders could cause a surge in violent crime, is already bogging down judges and attorneys, who are faced with identifying which offenders still in prison should be considered for reduced sentencing.

“It’s a tremendous amount of work to sort this all out,” the lead attorney for the Federal Defenders of New York, Leonard Joy, said.

As of Monday, the Sentencing Commission had identified 45 crack cocaine offenders convicted in federal courts in the city as being eligible for immediate retroactive release. In total, the commission has identified 381 offenders who could be resentenced in New York City federal courts in the coming years as a result of the decision.

Once defense lawyers determine which defendants are eligible for shortened sentences, judges must decide on a case-by-case basis whether offenders will be released from prison.

While judges will be expected to follow strict guidelines for shortening sentences, such as determining the potential danger an offender could pose to public safety, the Justice Department had sought more concretely to restrict those eligible for resentencing.

“We had hoped to tailor the rule to apply only to those who are first-time or nonviolent offenders — rather than all 19,500 eligible offenders — but that did not happen. We will be urging the courts not to go beyond the limited reduction that the Sentencing Commission has asked for and not to resentence defendants from scratch,” a spokeswoman for the Justice Department, Laura Sweeney, said.

The disparity between the punishments for crack cocaine, a drug used associated primarily with blacks, and powder cocaine, a drug more associated with whites, had led advocates to fight to reduce the prison terms for crack offenders. Currently, possession of a gram of crack cocaine mandates the same minimum sentence as that of 100 grams of powder cocaine.