Attorney General Eric H. Holder Jr. has ordered a review of a little-known Bush administration policy requiring some defendants to waive their right to DNA testing even though that right is guaranteed in a landmark federal law, officials said.

The practice of using DNA waivers began several years ago as a response to the Innocence Protection Act of 2004, which allowed federal inmates to seek post-conviction DNA tests to prove their innocence. More than 240 wrongly convicted people have been exonerated by such tests, including 17 on death row.