By Julia Edwards

WASHINGTON (Reuters) - Lowering prison sentences for non-violent drug offenders appeared to have few opponents in a U.S. Senate judiciary committee hearing on Monday, a sign of the waning influence of police groups and unions in the debate over prison reform.

The lone dissenter at the hearing, Republican Senator Jeff Sessions, raised concerns of law enforcement groups and argued on their behalf that lowering sentences would lead to higher crime rates.

Deputy Attorney General Sally Yates disagreed, pointing to states that have lowered the sentences of drug offenders without seeing a spike in crime.

Police groups and unions were once seen as a major obstacle to rethinking the policies that led to the United States having the highest incarceration rate in the world.

Senators who once sided with law enforcement on the issue have switched sides in recent months. Republican committee chair Charles Grassley, who once raised concerns about lowering mandatory minimum sentences, authored the bill now under consideration, the Sentencing Reform and Corrections Act.

But with crime rates down, federal support for police has plunged, prompting hiring freezes or layoffs in departments across the United States in recent years. In 1998, the Justice Department sent $1.4 billion to police through a grant program known as COPS. By 2014 that had dropped to $127 million.

"Our voice has been diminished," said Jonathan Adler, former president of the Federal Law Enforcement Officers Association, a non-union group of federal police. Adler blamed the "naive minds in denial over the real risks posed by drug peddlers."

Adler, who left his post last month but remains vocal on this issue, has been among police leaders who fear that reducing sentencing standards could lead to rising crime rate.

Police groups' position on the bill has been widely seen as crucial to its prospects. To win their support early on, authors of the bill in Congress and some officials in the Justice Department told police groups that money saved from reducing prison populations would go to local and state police.

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But that looks uncertain now. As introduced on Oct. 1, the bill makes no such promises.

"They put out a carrot, but it's a fake carrot," said Jim Pasco, executive director of the Fraternal Order of Police, the largest U.S. law enforcement union.

Deputy Attorney General Yates argued that over-spending on prisons subtracts from funds for police while not committing to backing specific appropriations.

"Every dollar we spend imprisoning a low-level non-violent drug offender for longer than he or she needs to be there is a dollar that cannot be spent on prosecutors and agents and cops on the street," Yates told the committee.

(Reporting by Julia Edwards; Editing by Kevin Drawbaugh and Lisa Shumaker)