OPM director John Berry said Friday that his staff has put a stop to $487 million of the $601 million in improper payments to deceased retired federal workers. And he pledged to quickly chase down the rest of the money.

“We’re hard at work on it,” Berry said in an interview. “It does require a vigorous effort.”

A report released Thursday by the agency’s inspector general revealed that the Office of Personnel Management had improperly distributed $100 million to $150 million in pensions and annuities in each of the last five years to families of federal employees who have died.

The government pays out $5.5 billion a month in retirement benefits to federal workers.

“There are bad people in the world who will commit fraud, and any program that is administering more than $5 billion a month in benefits needs strong controls,” Berry said.

The payments have been made since at least 2005, when Inspector General Patrick E. McFarland issued the first of three audits that urged OPM to track its mistakes more closely.

Berry said he is working “closely” with the inspector general’s staff and has set up better controls to make sure payments are legitimate. He said $113 million still needs to be resolved. He has assigned four members of his senior staff to deal with the issue.

Berry did not say how much of the nearly $487 million in payments was recouped for taxpayers and how much could not be found.