Justice Department officials announced Friday that 3,100 inmates are being released from federal prisons nationwide because of a change in how their good-behavior time is calculated — a significant step, they said, in the implementation of a new criminal justice reform law.

The announcement came at a news conference to discuss the Trump administration’s progress on putting into place the First Step Act, a criminal justice reform bill President Trump signed into law in December. Officials also announced they were redirecting $75 million in funding for fiscal year 2019 to help with implementation of both the act and a system to assess inmates’ risk of reoffending and provide tailored programming that could help them get out earlier.


‘‘The department intends to implement this law forcefully, fully and on time,’’ Deputy Attorney General Jeffrey Rosen said.

The First Step Act is one of the signature pieces of legislation passed during the Trump administration with bipartisan support. It shortens sentences for some inmates — partly through a change in the credit they are given for good behavior — and increases job training and other programs. It also requires the new risk assessment system, which officials said Friday will allow inmates to complete in-prison programs and, for some, receive ‘‘earned time’’ credits to get out earlier.

Associate Deputy Attorney General Antoinette Bacon said the largest portion of the 3,100 inmates being released are drug offenders, though the group also includes those convicted of weapons and sex offenses, robbery, and national security-related crimes. They are scattered across the country, and will probably all be out of Bureau of Prisons custody by Saturday, officials said.

Since the act’s passage, Rosen said, 1,691 people convicted of crack cocaine offenses also have received sentence reductions. That is because the measure retroactively applied a different sentencing law meant to resolve the disparity between penalties for those convicted of possessing crack cocaine and those convicted of possessing powder cocaine.