But others say releasing offenders early will only increase crime. Bill Otis, a former federal prosecutor and outspoken opponent of softened drug laws, attacked the early-release program in a blog post on Friday. “When these people start up with a criminal life again, as we know in advance many and very likely most of them will,” he wrote, “who will be accountable for the release decisions, and who will pay the price for the harm then caused?”

Of 6,112 being released in the initial group, 1,764 are noncitizens who will transfer to the custody of immigration officials. Of the 4,348 others, nearly 80 percent are already outside prison walls, the Justice Department said — living in halfway houses which they may leave for jobs and counseling, or under home confinement that allows them to move about within strict limits.

Virtually all of those released will face years of supervision by a probation officer.

The current bubble in releases has stretched the country’s halfway houses, with some prisoners not landing spots, and may temporarily strain probation offices, federal defenders and justice officials say. But they also note that more than 1,000 inmates are routinely released from federal prison each week, and more than 10,000 a week from state prisons.

A total of 46,000 current federal drug prisoners are eligible for resentencing, according to the commission, but so far, judges have turned down about one in four applicants.

In any case, researchers say, the effect on total federal prisoners, now some 205,000, will be small, pulling the total down by a few percentage points. Modest additional reductions in the federal prison population will be achieved if bills now before Congress, to reduce the use of mandatory minimums and other measures, are adopted.

Still, any cut in prison terms at all is precious to inmates, Mr. Keating and other former prisoners said. Mr. Keating knows he is luckier than many of his fellow prisoners, especially because he has a supportive family.

Mr. Keating was 22 and addicted to methamphetamine when he was arrested and charged with production because, he said before pleading guilty, he had allowed others to produce the drug on his land in return for a free supply.