A judicial panel voted Friday to slash prison time for thousands of inmates — hundreds of them from Maryland — a significant move toward softening the severe punishments for federal drug crimes.

If the step by the U.S. Sentencing Commission is not blocked by Congress, about half of the federal prisoners incarcerated for drug crimes — about 46,000 people — will be eligible for sentence reductions averaging more than two years.

The vote is the latest in a string of triumphs for advocates of shorter sentences as the country grapples with how to deal with a federal prison population that has swelled under decades-old laws. But even after the other victories, some advocates of reduced sentences called Friday's shift the biggest in more than 20 years.

The commission had decided in April to reduce future sentences. Friday's vote extends the same approach retroactively to those serving time. Releases could begin starting Nov. 1, 2015.

Until then, defense attorneys in Maryland and across the country will be rushing to court to file petitions on behalf of inmates. It will be up to U.S. attorneys to respond to the cases and battle over whether an inmate's early release will pose a threat to public safety.

James Wyda, head of the Maryland federal public defender's office, said his team will handle most of the cases, and he praised the move.

"This is another step — perhaps the most wide-ranging and important step — in the process to reform our far too severe federal drug sentencing laws," he said. "These excessive sentences have been imposed mostly against poor people, mostly people of color.

"This is a very good day for fairness and justice in our federal courts."

An analysis by the sentencing commission found about 600 inmates from Maryland who would be eligible for early release. Wyda said he thinks the number could be even higher.

The basis of federal drug sentencing policy was set out in a 1986 law that Congress quickly passed after University of Maryland basketball star Len Bias died of a cocaine overdose. The university announced this week that he would be inducted into its sports hall of fame. The law spelled out often-stiff minimum sentences for drug distribution that sometimes reached even lower-level dealers.

In recent years, all branches of the federal government have been working out ways to rethink the lengthy sentences that law introduced. In 2010, Congress voted to reduce the disparity between prison terms for crack and powder cocaine. Congress is weighing further changes.

The sentencing commission, which is part of the judiciary, has also cut back on recommended prison terms for some types of cases. And the federal public defenders have slogged through the courts, winning cases to get prisoners released.

Attorney General Eric H. Holder Jr. has generally been an advocate of such reductions. The Justice Department originally asked the commission to take a narrower approach — one that would affect just 20,000 inmates — but Holder said Friday he supports the new policy.

The department was able to postpone the effective date of the change for a year to give prosecutors time to weed out inappropriate cases, an official said.

U.S. District Judge Patti B. Saris, chairwoman of the commission, a group of judges and lawyers who establish sentencing policies, said the amendment won support because it was a "measured approach."

"It reduces prison costs and populations, and responds to statutory and guidelines changes since the drug guidelines were initially developed, while safeguarding public safety," she said.

But not all authorities are supportive of the new guidelines.

"The strong sentencing scheme that has been in place in place over the last 25 years in our country has contributed to the lowest crime rates in more than a generation," the National Association of Assistant United States Attorneys said in a statement.

Inmates eligible to apply for a reduction are not guaranteed release under Friday's move.

None would be let out until a judge reviews their case to determine whether a reduced sentence poses a risk to public safety. The sentencing commission analysis projected that the releases will be spread out over the next six or more years.

The House and Senate would have to vote by Nov. 1 to block the plan. But there has been bipartisan support in both houses for broad changes in prison policies, and Obama administration officials do not expect a concerted effort to change the commission's new policy.

A study of previous early releases of drug offenders found no effect on recidivism rates.

"There is little evidence to suggest that excessively punitive federal drug policies have improved public safety," said Mark Mauer, head of advocacy group the Sentencing Project.

"Today's commission vote represents a major milestone in bringing a greater measure of rationality to federal drug sentencing."

Tribune newspapers Washington correspondent Timothy M. Phelps contributed to this article.

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