Attorney General Eric H. Holder Jr. is reversing a controversial Bush administration policy under which numerous defendants have waived their right to DNA testing even though that right is guaranteed under federal law, Justice Department officials said Wednesday.

Holder will issue a memo on Thursday to the nation's 93 U.S. attorneys, which overturns the practice of seeking "DNA waivers,'' said the officials, who spoke on condition of anonymity because the policy shift had not been publicly announced.

The waivers have been in widespread use in federal cases for about five years and run counter to the national movement toward allowing prisoners to seek post-conviction DNA testing to prove their innocence. More than 260 wrongly convicted people have been exonerated by such tests, though virtually all have been state prisoners.

The waivers are filed only in guilty pleas and bar defendants from ever requesting DNA testing, even if evidence emerges that could exonerate them. Statistics show that innocent people sometimes plead guilty, often for a reduced sentence. One quarter of the 261 people who have been exonerated by DNA testing had falsely confessed to crimes they didn't commit, and 19 of them pleaded guilty, according to the New York-based Innocence Project.

Holder last year ordered a review of the little-known policy, under which the Bush Justice Department had told prosecutors to seek DNA waivers whenever possible. The review came after inquiries about DNA waivers by The Washington Post.

The waivers have been part of the standard plea agreement filed by some of the nation's most prominent U.S. attorneys, including those in the District, Alexandria and Manhattan. Defense lawyers say their clients are essentially forced to sign the waivers or lose the benefits of a plea agreement, such as a lighter sentence.

Holder's memo, according to sources who have seen it, says the DNA waiver policy is rigid and inconsistently applied. As of last year, at least 19 U.S. attorneys' offices used the waivers for some or all plea agreements, while 24 U.S. attorneys did not use them. It could not be determined how many inmates have been affected by the policy, because the remaining U.S. attorneys' offices did not respond to inquiries or declined to comment.

Now, Holder's memo says prosecutors can only seek the waivers in extraordinary circumstances and with a supervisor's approval, the sources said.

Defense lawyers and DNA advocates welcomed the Justice Department's reversal, saying that denying prisoners the ability to prove their innocence violates a fundamental right.

"It never made any sense to force people, as a condition of a plea, to give up their right to future DNA testing, particularly since we know that factually innocent people plead guilty,'' said Peter Neufeld, co-founder of the Innocence Project. While few federal prisoners have sought post-conviction DNA testing, in part because of the waiver policy, Neufeld expects that number to rise.

Steve Benjamin, a Richmond lawyer who is vice president of the National Association of Criminal Defense Lawyers, called Holder's decision "a no-brainer. There should never be any bar to a person's ability to establish their innocence.''

He added that using the waivers in guilty pleas had essentially "gutted" the Innocence Protection Act of 2004, a law that for the first time allowed federal inmates to seek post-conviction DNA tests to prove their innocence. Government statistics show that more than 95 percent of federal convictions result from guilty pleas.

Interviews and documents show that the DNA waiver policy arose in response to the 2004 law, proposed by Sen. Patrick J. Leahy (D-Vt.). Language allowing for DNA waivers was inserted into the law at the behest of Republican senators, congressional sources said, and the Bush Justice Department lobbied against the measure, even with the waiver provision.

Soon after the law passed with bipartisan support, the department sent a secret memo in November 2004 to the nation's U.S. attorneys directing them to seek the waivers, according to federal officials who have seen the memo.

Prosecutors who use the waivers have said that guilty pleas should be final and that those who have admitted guilt should not be able to file frivolous petitions for testing. They say the wave of DNA exonerations has little impact in federal court because nearly all of those found to be innocent were state prisoners, and the waivers apply only to federal charges. DNA evidence is used far more frequently in state courts.

But DNA experts have said that is about to change because more sophisticated testing will soon bring biological evidence into federal courtrooms for a wider variety of crimes. And last year, a District man, Donald Eugene Gates, became the first federal inmate exonerated by DNA testing. He had been jailed for 28 years in the rape and murder of a Georgetown University student, until DNA evidence revealed that another man committed the crime.

Holder, a former U.S. attorney in the District who has called for expanded DNA testing in federal courts, will also issue another memo on Thursday clarifying Justice Department guidelines for collecting DNA samples from federal prisoners, sources said.

"The attorney general believes it's important that we use DNA to the greatest extent possible to solve crimes,'' said one Justice Department official, "and these polices will ensure we can do that.''