SAN FRANCISCO — Ushering in a significant shift in the nation’s four-decade “war on drugs,” Attorney General Eric Holder said Monday that federal prosecutors will stop seeking longer mandatory sentences for many nonviolent drug offenders, part of a broad new effort to focus on violent crimes and national security while reducing the nation’s gigantic prison population.

In a speech at the American Bar Association’s annual meeting, Holder said the Justice Department would promote drug-treatment and community-service programs as alternatives to prison for many low-level offenders who for years have been caught up in the same strict federal sentencing laws aimed at gang members and drug kingpins.

“By reserving the most severe penalties for serious, high-level or violent drug traffickers, we can better promote public safety, deterrence and rehabilitation, while making our expenditures smarter and more productive,” Holder said.

The new strategy would only apply in the federal justice system — where 47 percent of prisoners are being held on drug convictions — but drug policy experts said the symbolism is far-reaching. As Holder pointed out, states across the country, including Texas and California, have re-examined drug enforcement and tough sentencing standards to thin out bulging prison populations.

While many drug policy reformers and civil rights advocates applauded the shift, calling it long overdue and a first step, some Republicans decried it as power play by the Obama administration.

In the 1980s, Congress enacted five- or 10-year mandatory minimum prison terms depending on the quantity of drugs, limiting judges’ ability to impose shorter sentences. But Holder said prosecutors will no longer list in indictments the amount of drugs found on nonviolent offenders who aren’t connected to gangs or cartels, a move that would avoid triggering the mandatory minimums.

Holder said the Justice Department also has expanded the criteria by which elderly inmates who no longer threaten public safety can seek compassionate early release. He’s also directing all U.S. Attorneys to create and update comprehensive anti-violence strategies for the areas hardest hit by violent crime.

“We must never stop being tough on crime. But we must also be smart and efficient when battling crime and the conditions and the individual choices that breed it,” he said.

Many drug offenses violate both federal and state law, leaving federal and state prosecutors to work out their own policies about who’ll prosecute which cases; the Justice Department typically has had little or no role in pursuing those accused of simple possession or even small possession-for-sale cases.

Drug-policy reform advocates have been calling for Congress to eliminate mandatory minimum sentencing laws for years, but said Holder’s move was a good first step.

“There’s no good reason why the Obama administration couldn’t have done something like this during his first term — and tens, perhaps hundreds of thousands of Americans have suffered unjustly as a result of their delay,” Ethan Nadelmann, executive director of the Drug Policy Alliance, said in a news release. “But that said, President Obama and Attorney General Holder deserve credit for stepping out now, and for doing so in a fairly decisive way.”

Will Matthews, spokesman for the American Civil Liberties Union of Northern California, said states must follow Holder’s lead and “once and for all abandon the failed and costly policies of the past … that have left far too many people locked up for far too long who don’t need to be kept behind bars to keep our families and communities safe.”

But House Judiciary Committee Chairman Bob Goodlatte, R-Va., said this is the latest case of the Obama administration “overstepping its constitutional bounds by selectively enforcing our laws and attempting to change them through executive fiat.” Though he agrees with many of the policies Holder spoke of Monday, the lawmaker said Holder should work with the “Overcriminalization Task Force” that the Judiciary Committee created months ago rather than acting unilaterally.

“While the Attorney General has the ability to use prosecutorial discretion in individual cases, that authority does not extend to entire categories of people,” Goodlatte said.

House Minority Leader Nancy Pelosi, however, said she has always opposed mandatory minimums and she commended Holder and Obama for their leadership. Pelosi, D-San Francisco, said she looks forward “to working on legislative efforts to eliminate mandatory minimum sentences once and for all.”

The United States accounts for about 5 percent of the world’s population, but about 25 percent of its prison inmates. The nation’s federal prison system has grown by 800 percent since 1980 and had 219,520 inmates as of last Thursday, 47 percent of whom are behind bars for drug offenses and 49 percent of whom are serving five to 15 years.

“Widespread incarceration at the federal, state, and local levels is both ineffective and unsustainable,” Holder said Monday. “It imposes a significant economic burden — totaling $80 billion in 2010 alone — and it comes with human and moral costs that are impossible to calculate.”

It’s also racially disproportionate, he noted, citing a February report showing that black male offenders in recent years have received sentences nearly 20 percent longer than those imposed on white males convicted of similar crimes.

“This isn’t just unacceptable: It is shameful,” Holder said, announcing he has directed a group of U.S. attorneys to study and suggest solutions to racial disparities in sentencing.

UC Berkeley law professor Robert MacCoun, a drug-policy expert, called Holder’s speech “tremendously symbolic” and “a sign that change is starting to take place,” though not as huge as eliminating mandatory minimums entirely would be.

Two-thirds of Americans sentenced for drug crimes are in state prisons and not subject to these sentencing reforms, MacCoun noted, but the attorney general has a high bully pulpit. Conservatives might view Holder with suspicion but there’s growing consensus that the old policies need to be changed, he said, and this new approach “can only help. It is not as if they are going to double mandatory minimums to spite him.”

Staff writer Daniel Willis contributed to this report. Contact Josh Richman at jrichman@bayareanewsgroup.com and follow him at Twitter.com/josh_richman. Contact Thomas Peele at tpeele@bayareanewsgroup.com and follow him at Twitter.com/thomas_peele.