WASHINGTON — Sometime in the next few weeks, aides expect President Obama to issue orders freeing dozens of federal prisoners locked up on nonviolent drug offenses. With the stroke of his pen, he will probably commute more sentences at one time than any president has in nearly half a century.

The expansive use of his clemency power is part of a broader effort by Mr. Obama to correct what he sees as the excesses of the past, when politicians eager to be tough on crime threw away the key even for minor criminals. With many Republicans and Democrats now agreeing that the nation went too far, Mr. Obama holds the power to unlock that prison door, especially for young African-American and Hispanic men disproportionately affected.

But even as he exercises authority more assertively than any of his modern predecessors, Mr. Obama has only begun to tackle the problem he has identified. In the next weeks, the total number of commutations for Mr. Obama’s presidency may surpass 80, but more than 30,000 federal inmates have come forward in response to his administration’s call for clemency applications. A cumbersome review process has advanced only a small fraction of them. And just a small fraction of those have reached the president’s desk for a signature.

“I think they honestly want to address some of the people who have been oversentenced in the last 30 years,” said Julie Stewart, the founder and president of Families Against Mandatory Minimums, a group advocating changes in sentencing. “I’m not sure they envisioned that it would be as complicated as it is, but it has become more complicated, whether it needs to be or not, and that’s what has bogged down the process.”