WASHINGTON — The Obama administration on Thursday expanded its effort to curtail severe penalties for low-level federal drug offenses, ordering prosecutors to refile charges against defendants in pending cases and strip out any references to specific quantities of illicit substances that would trigger mandatory minimum sentencing laws.

The move, announced by Attorney General Eric H. Holder Jr. at a speech before the annual conference of the Congressional Black Caucus, builds on a major policy change he unveiled last month to avoid mandatory minimum sentencing laws in future low-level cases.

“By reserving the most severe prison terms for serious, high-level, or violent drug traffickers or kingpins, we can better enhance public safety,” Mr. Holder said. “We can increase our focus on proven strategies for deterrence and rehabilitation. And we can do so while making our expenditures smarter and more productive.”

The policy applies to defendants who meet four criteria: their offense did not involve violence, the use of a weapon, or selling drugs to minors; they are not leaders of a criminal organization; they have no significant ties to large-scale gangs or drug trafficking organizations; and they have no significant criminal histories.