Attorney General Eric H. Holder Jr.’s proposed prison reforms drew praise from criminal justice experts Monday, but some critics said the proposals do not go far enough to begin overhauling a costly and broken law enforcement system.

In an effort to reduce the population of the nation’s overflowing ­federal prisons, Holder directed his 94 U.S. attorneys across the country to stop charging low-
level, nonviolent drug offenders
with offenses that impose severe mandatory sentences.

The disparities in the criminal justice system unfairly hit poor and minority communities the hardest, Holder said in a speech at the annual meeting of the American Bar Association in San Francisco. Holder cited a recent “deeply troubling report” that indicates that black male offenders have received sentences nearly 20 percent longer than those imposed on white males convicted of similar crimes.

“This isn’t just unacceptable,” Holder said. “It is shameful.”

Many of Holder’s proposals, which are aimed at saving tens of millions in prison costs, have bipartisan support, and the Obama administration does not expect them to be politically controversial. In fact, there is strong conservative backing for reforming prisons and mandatory minimum laws, and Republican governors in some of the most conservative states have led the way on prison reform.

Drug offenses account for 17%, or nearly one in five, of those in state prisons, according to national incarceration data.

In Congress, both Republican and Democratic leaders have introduced legislation aimed at giving federal judges more discretion in applying mandatory minimums to certain drug offenders.

Laura W. Murphy, director of the American Civil Liberties Union’s Washington Legislative Office, said the ACLU is “thrilled” by Holder’s actions.

“These policies will make it more likely that wasteful and harmful federal prison overcrowding will end,” Murphy said.

Sen. Rand Paul (R-Ky.) said he was heartened by the Obama administration’s willingness to review mandatory minimum sentencing. But Sen. Charles E. Grassley (R-Iowa), said the law should be changed only in conjunction with Congress.

“The overreach by the administration to unilaterally decide which laws to enforce and which laws to ignore is a disturbing trend,” Grassley said.

Holder cited figures that show the federal prison population has grown almost 800 percent since 1980. “With an outsized, unnecessarily large prison population, we need to ensure that incarceration is used to punish, deter and rehabilitate, not merely to warehouse and forget,” he said.

Lawyers across the Washington region said many questions remain about how Holder’s proposals will be implemented.

Matt Kaiser, a former public defender in Greenbelt and an adjunct professor of law at Georgetown University, applauded Holder for talking about “mass incarceration.”

“The problem is that when you look at why we have so many people in prison — especially at the federal level — what he is proposing is not likely to . . . reduce those numbers,” Kaiser said.

Ronald C. Machen Jr., the U.S. attorney for the District of Columbia, said his office is evaluating when it is appropriate to seek a mandatory minimum sentence.

“We look forward to implementing the Department’s new guidance in a manner that conserves our resources so that we can best confront our most pressing and persistent public safety challenges,” Machen said in a statement.

Jeffrey Zimmerman, an Alexandria defense lawyer, said Holder’s memo had “rocketed around the defense community” and could undercut an argument prosecutors often make in negotiating plea deals — that their hands are tied by “office policy.”

Zimmerman said that while the policy change probably would not affect those already sentenced, it would put the brakes on defendants about to agree to plea deals that might bind them to mandatory minimum terms.

Michael Nachmanoff, the federal public defender for the Eastern District of Virginia, said he initially was encouraged by Holder’s guidance. Still, Nachmanoff said, he remained skeptical of whether the directive actually would restrain prosecutors in deciding how to charge their cases.

“There’s a real difference between general guidance from the attorney general and actually taking actions on the ground,” Nachmanoff said. “Mandatory minimums are a very powerful tool for federal prosecutors.”

Julie Stewart, president of Families Against Mandatory Minimums, said that Holder’s proposals are a “great step in the right direction” but added that “what’s being proposed here is very modest.”

“These are minor tweaks compared to the major overhauls we’ve seen enacted at the state level,” Stewart said.

Indeed, Holder pointed to recent state initiatives as models for significant national prison reform.

In Kentucky, new legislation has reserved prison cells for the most serious offenders, instead focusing resources on community supervision and other alternatives. The state is projected to reduce its prison population by more than 3,000 over the next 10 years, saving more than $400 million, according to Justice Department officials.

Investments in drug treatment for nonviolent offenders and changes to parole policies in Texas reduced the prison population by more than 5,000 inmates last year. Similar efforts helped Arkansas reduce its prison population by more than 1,400 last year.

“Clearly, these strategies can work,” Holder said. “They’ve attracted overwhelming, bipartisan support in red states as well as blue states. And it’s past time for others to take notice.”

Keith Alexander contributed to this report.