WASHINGTON (Reuters) - A criminal justice bill awaiting a vote by the U.S. Senate would reduce federal prison costs by $722 million over the next 10 years by releasing thousands of federal prisoners early, congressional forecasters said on Wednesday. Federal benefits received by the newly released prisoners would increase direct spending by $251 million and reduce revenues by $8 million over the same period, according to the estimate by the U.S. Congressional Budget Office. The new savings estimate buoyed supporters of the bipartisan measure to lower mandatory minimum sentences for some non-violent federal drug offenders, which is central to President Barack Obama’s efforts to overhaul the country’s federal criminal justice system and reduce prison overcrowding.  “We have an obligation to change the way we think about incarceration, and today’s CBO report shows that we have a fiscal obligation as well,” said the bill’s co-authors, U.S. senators Charles Grassley, a Republican from Iowa, and Richard Durbin, a Democrat from Illinois, in a statement. The bill was revised last month to exclude prisoners convicted of violent crimes in an effort to garner more support among conservatives.  Still, its prospects for moving to a full Senate vote remain unclear. Some key Republican senators are reluctant to support the bill until it includes changes to “mens rea” laws that govern criminal intent.  Parallel sentencing reforms await a floor vote in the U.S. House of Representatives. A White House study last month found that current sentencing and incarceration policies strain state budgets, take people out of the work force and pull families apart more than they reduce crime or boost the U.S. economy. (Refiles to fix misspelling of “mens rea” in sixth paragraph.) 