Federal prosecutors will withdraw key documents from their case against a former National Security Agency manager charged with mishandling classified material, a move that experts say could signal the unraveling of one of the Obama administration’s most prominent efforts to punish accused leakers.

Prosecutors informed U.S. District Judge Richard Bennett this week that they would withhold documents they had planned to introduce as evidence to keep from disclosing sensitive technology. Former NSA executive Thomas A. Drake is charged with unlawfully retaining classified information at a time when he was in touch with a Baltimore Sun reporter who later chronicled mismanagement at the agency.

The government has used the 1917 Espionage Act, which has been criticized as vague and overbroad, to charge Drake, one of five such cases against alleged leakers under the Obama administration. Drake is not accused of spying, but the law’s provisions criminalize the unauthorized retention of classified material. The trial is set to begin Monday.

The government’s decision to withhold certain documents may complicate prosecutors’ efforts to prove a violation of the act, suggesting that the government may have overreached in using an espionage law to target a suspected leaker.

“By withdrawing several of the exhibits, at least a couple of the counts against Drake will almost certainly need to be dismissed,” said Steven Aftergood, a national security expert with the Federation of American Scientists who has followed the case closely since Drake was indicted last year. “It changes the whole dynamic of the prosecution and may even set the stage for settlement or dismissal.”

Thomas Drake is charged with mishandling classified files. (Jacquelyn Martin/ASSOCIATED PRESS)

Prosecutors “gambled that the court would permit them to submit unclassified substitutions for this information,” Aftergood said. “The case isn’t over, but this is clearly a setback for the prosecution.”

Transparency activists and media experts warn that such prosecutions could stanch the flow of information the public needs to judge policy, and George W. Bush administration officials see the prosecutions as selective — ignoring high-level officials who release sensitive information to advance their personal or policy agendas.

Justice Department spokesman Laura Sweeney declined to comment on the case.

Drake, 54, could face 35 years in prison if convicted of “willful retention of national defense information.” He is not charged with a leak.

Drake has said that he is a whistleblower who is facing a politically motivated reprisal for drawing attention to the NSA’s inefficiencies. “I will never plea-bargain with the truth,” he told friends last year.

Drake was a senior executive at the NSA — a “senior change leader” — who professed an ambition to change the agency’s insular culture. He became disillusioned with the agency’s handling of major technology programs and concerned that the NSA was needlessly violating Americans’ privacy through a massive surveillance program adopted after the Sept. 11, 2001, terrorist attacks. He raised concerns with officials and the inspector general, and later with the reporter, before leaving the agency in 2008.

According to people following the case, the government may have to drop two Espionage Act counts that relate to information that Drake submitted to the Defense Department inspector general between 2002 and 2004 to buttress colleagues’ complaints about waste, fraud and abuse of a bungled NSA data-sifting program, Trailblazer. He and his former NSA colleagues thought the complaints were confidential.

The evidence for those two counts is contained in Exhibits 42 and 43, according to the sources. Prosecutor William M. Welch II, in a letter Sunday to Bennett, a U.S. District Court judge in Baltimore, said those exhibits will be withdrawn. The letter was first reported by Politico.

Another exhibit, numbered 41, also consisting of information Drake submitted to the inspector general, is intended to support a third Espionage Act count, which may also be dropped, the sources said. That exhibit will be redacted, the prosecution has said.

Two remaining Espionage Act charges relate to information that Drake possessed but that had been published on the NSA’s in-house intranet. Legal experts said Drake could contend that the material was unclassified information that was widely available to tens of thousands of agency employees.

The rest of the charges — one count of obstruction of justice and four counts of making a false statement — are less important, legal experts said.

Prosecutors decided to withdraw and redact the documents after Bennett ruled that they could not substitute unclassified language without harming Drake’s ability to mount a defense.

In his letter, Welch, who led the unsuccessful corruption prosecution of the late senator Ted Stevens (R-Alaska), stated he was withdrawing four exhibits and redacting two more to remove any reference to a “particular telecommunications technology.”

“In short, no reference to the technology will be made,” Welch said. “This will allow continued protection of the details of NSA’s efforts in this area, while simultaneously protecting the defendant’s constitutional ability to present his defense.”

The case against Drake is already leaner than initially planned. Welch’s predecessor, Steven Tyrrell, had wanted to charge Drake with leaking classified documents to a reporter and being part of a conspiracy, according to an early draft of the indictment that Welch inadvertently sent to the defense team.

Leak prosecutions under the Espionage Act had been relatively rare until the Obama administration. Daniel Ellsberg, who gave the Pentagon Papers to a reporter, was the first leaker indicted under the law, but his case ended with a mistrial after government misconduct.

The Obama administration is presiding over five cases involving the act, including those against Pfc. Bradley Manning, a former Army intelligence analyst accused of passing State Department and military war data to the anti-secrecy Web site WikiLeaks; Stephen Kim, a former State Department analyst accused of leaking to a television reporter; and Jeffrey Sterling, a former CIA analyst accused of passing classified information to author and New York Times reporter James Risen.

“Obama is prosecuting whistleblowers who made the kinds of disclosures that he said he wants — contractors bilking the government of billions of dollars,” said Jesselyn Radack, a former Justice Department whistleblower and director of national security at the Government Accountability Project. “That’s what Drake did.”

Staff researcher Julie Tate contributed to this report.