The US Sentencing Commission has voted unanimously to begin a sweeping review of federal sentences for drug dealers in a move that could herald long-awaited reductions in America's prison population.

Just days after attorney general Eric Holder called for a new approach to the so-called "war on drugs", the commission met in Washington to agree a new policy priority that potentially goes far further than the Department of Justice can in lowering sentences.

As anticipated, the independent government agency, which issues sentencing guidelines to federal judges, will now spend the next few weeks reviewing its "drug quantity table" – the grid that determines prison lengths for dozens of different categories of offence – before publishing new recommendations in January.

A reduction in sentencing guidelines could still be blocked by Congress, but Holder's speech on Monday has coincided with a new mood of reform in Washington that reverses decades of political pressure to increase penalties for drug dealers. His comments were welcomed by Senate judiciary committee chair Patrick Leahy and leading Republicans such as senator Rand Paul.

Currently the guidelines in the commission's drug quantity table can result in first-time offenders facing sentences of 19 to 24 years, with no parole, for possession of the maximum quantities of heroin, crack or methamphetamine. Even dealers caught with 100g of cocaine can face between 27 and 33 months, according to the table.

A number of specific offences are also subject to mandatory minimum sentences prescribed by Congress, although Holder instructed US prosecutors on Monday to begin circumventing such automatic terms by changing the way they bring charges.

The seven commissioners who voted on the sentencing panel, including five senior judges, are now thought likely to go much further than this by formulating across-the-board changes to the recommended sentences.

Speaking afterwards, Dabney Friedrich, a former associate counsel in the Bush White House who sits on the commission, told the Guardian she thought that pressure in Congress to control the cost of the US prison system would be a key factor in ensuring political support for such a move.

The Department of Justice also issued a supportive statement on Thursday, which welcomed the commission's progress.

"As the attorney general expressed earlier this week, we think there is much to be done to improve federal sentencing and corrections," said DOJ official Jonathan Wroblewski. "Moreover, we think the US Sentencing Commission has a very big role to play in shaping that reform."

In a statement issued after its meeting, the commission noted that drug offenders account for nearly half of all federal inmates, and that "an adjustment to the drug quantity tables in the sentencing guidelines could have a significant impact on sentence lengths and prison populations."

"With a growing crisis in federal prison populations and budgets, it is timely and important for us to examine mandatory minimum penalties and drug sentences, which contribute significantly to the federal prison population," added Judge Patti Saris, chair of the commission.

"The Commission is looking forward to a serious and thoughtful reconsideration of some of the sentencing guidelines which most strongly impact the federal criminal justice system," she said. "I am glad that members of Congress from both parties and the Attorney General are

engaged in similar efforts."

The Commission also pledged to work with Congress to reduce the "severity and scope of mandatory minimum penalties and consider expanding the 'safety valve' statute which exempts certain low-level non-violent

offenders from mandatory minimum penalties". It will pass its final amendments to Congress in May.

Political reaction to the recent sentencing developments has been broadly positive. Senator Leahy said was pleased at Holder's call for a review of mandatory minimum sentences.

Although he believes long sentences are appropriate in some cases, but the veteran Democrat said it believes judges should be given more flexibility rather than relying on mandatory requirements.

Others have expressed concern however at the new mood sweeping Washington.

William Otis, a former federal prosecutor at Georgetown University, said stiffer sentences in recent decades had contributed to lower crime rates.

"Two generations ago, in the 1960s and 1970s, our country had the wholly discretionary sentencing system Holder admires. For our trouble, we got a national crime wave," he wrote in a USA Today op-ed.

"We have every right to instruct judges that some offenses are just too awful to allow an overly sympathetic jurist to burst through a congressionally established floor."