The Obama administration sees that trend as a reflection of more lenient and sensible approaches to sentencing, and in recent months, Justice Department officials have moved ahead with initiatives meant to provide “second chances” for criminal offenders and ease their path back to their communities.

They set up a school system in federal prisons. They put in place new oversight for halfway houses. They created a new, centralized mental health facility for women at the federal prison in Danbury, Conn. They stopped using private prisons to house federal offenders because of safety and security concerns. And they issued a report in conjunction with the Urban Institute concluding that fairer and “more enlightened” prison sentencing policies at the state level — where the bulk of prisoners are held — had succeeded both in bolstering public safety and in cutting many millions in costs for strapped states.

Many of the recent initiatives have not made headlines, but they have contributed to what Justice Department officials see as a cultural shift that began under Mr. Obama’s first attorney general, Eric H. Holder Jr., who instituted a policy in 2013 meant to lessen potential sentences for nonviolent drug offenders.

Deputy Attorney General Sally Yates, who has led many of the prison initiatives, has sought to send the message that locking people up is not the department’s sole mission. “We’re not the Department of Prosecution,” aides said she often reminded them. “We’re the Department of Justice for a reason.”

Daryl Atkinson, a lawyer from Alabama, is one reflection of that attitude. He spent more than three years in federal prison in the 1990s on a first-time drug trafficking conviction, but he went on to get a degree in law and is now working at the Justice Department as its initial “Second Chance Fellow,” part of a new program reserved for former prisoners. “To me, the fellowship is a testament to the fact that the administration is really walking the walk,” Mr. Atkinson said in an interview. “This shows people with records that opportunities are still open to them.”

Ms. Lynch and her deputy, Ms. Yates, were both longtime federal prosecutors, and as a prosecutor in Brooklyn in the 1990s, Ms. Lynch tried many drug cases at a time when narcotics offenders nationwide faced long prison sentences, particularly for crack cocaine, which was much more commonly used among blacks.

The mentality among prosecutors at the time was to put drug offenders away for as long as possible. But Ms. Lynch said the stiff sentencing policies failed to adequately distinguish between the drug kingpin and “the kid on the corner.”