President Obama and first lady Michelle Obama depart the White House on Monday. (Chip Somodevilla/Getty Images)

President Obama on Tuesday commuted the sentences of 22 drug offenders, the largest batch of prisoners to be granted early release under his administration as it steps up an overhaul of the nation’s criminal justice system.

The early release of federal inmates is part of a sweeping effort to reduce the enormous costs of overcrowded prisons and address drug sentences handed down under old guidelines U.S. officials now view as too harsh. Obama had previously commuted the sentences of eight prisoners under the new Justice Department-led initiative; tens of thousands more are seeking to have their cases reviewed.

The 22 inmates whose sentences were commuted Tuesday were nonviolent offenders serving time for the possession, sale and distribution of substances including methamphetamine, marijuana and cocaine. One, Terry Andre Barnes of East Moline, Ill., was convicted of conspiracy to distribute cocaine and sentenced in July 2005 to 246 months in prison, a term that would have kept him behind bars until 2025.

Obama wrote a letter to each of the inmates — all but one of whom, including Barnes, will be released July 28 — urging them to use the opportunity to rebuild their lives.

“I am granting your application because you have demonstrated the potential to turn your life around. Now it is up to you to make the most of this opportunity,” Obama wrote. “It will not be easy, and you will confront many who doubt people with criminal records can change. . . . But remember that you have the capacity to make good choices.”

“I believe in your ability to prove the doubters wrong,” the president concluded, “So good luck, and Godspeed.”

White House counsel Neil Eggleston said that under current sentencing guidelines, many of the individuals granted clemency would have already served their time in prison.

“Because many were convicted under an outdated sentencing regime, they served years — in some cases more than a decade — longer than individuals convicted today of the same crime,” Eggleston said in a blog post outlining the reasoning behind the commutations, adding that they “underscore the president’s commitment to using all the tools at his disposal to bring greater fairness and equity to our justice system.”

Since the Obama administration announced last year that it would grant clemency to nonviolent offenders, more than 35,000 inmates — about 16 percent of the federal prison population — have applied to have their sentences shortened.

The process has been slow to get off the ground. More than 1,500 volunteer lawyers working with the Clemency Project 2014 — a group that includes Families Against Mandatory Minimums, the American Civil Liberties Union, the American Bar Association and the National Association of Criminal Defense Lawyers — have been sifting through the applications to help identify candidates for early release and to represent them.

Under the Justice Department criteria released last spring, candidates for clemency must have served at least 10 years of their sentence, have no significant criminal history and no connection to gangs, cartels or organized crime. Inmates who apply must be prisoners who probably would have received a “substantially lower sentence” if convicted of the same offense today.

Some of the inmates whose sentences Obama commuted on Tuesday were prisoners whose applications were supported by Clemency Project lawyers.

“I cannot express in stronger terms how gratifying it is to see today’s grants of clemency by the White House,” said Cynthia W. Roseberry, project manager for Clemency Project 2014. “I hear every day from prisoners and their loved ones who for the first time in many years have hope. For far too long, this nation went down the road of locking up nonviolent offenders and throwing away the keys, without any regard for value of these people and the damage that mass incarceration does to families, communities and to our entire society.”

While many criminal justice activists have criticized Obama for not doing more to pardon low-level offenders, Eggleston noted that, with Tuesday’s action, the president has now granted 43 commutations.

“To put President Obama’s actions in context, President George W. Bush commuted 11 sentences in his eight years in office,” he wrote, adding that Obama remains committed to pursuing broader criminal justice reform through bipartisan legislation.

While Republicans and Democrats remain at an impasse on many issues, one of the few legislative initiatives that has the potential of passing this year is a bill overhauling the nation’s sentencing guidelines.