A critical moment in the United States’ case against former National Security Agency official Thomas A. Drake came a week ago Friday, when a federal judge ruled that the prosecution could not shield from public disclosure classified information it wanted to present as evidence.

So the prosecutors, rather than reveal what the NSA considered sensitive material, withdrew their proposed exhibits.

That decision effectively doomed the government’s effort to put Drake behind bars for as many as 35 years for unlawfully retaining classified information. As the prosecution crumbled, so went the government’s opportunity to turn Drake’s case into a cautionary tale for would-be leakers.

On Friday, Drake accepted lead prosecutor William M. Welch II’s offer to plead guilty to a single misdemeanor of misusing a government computer to provide information to an unauthorized person. Drake is expected to serve no prison time.

“This is a just result,” said Debbie Boardman and Jim Wyda, Drake’s attorneys, in a statement. “Tom Drake should never have been charged under the Espionage Act. Tom never intended to harm his country. And he didn’t.”

The Drake case exposes a fundamental dilemma in prosecutions involving national security: How do you prove that a leaker released sensitive information without discussing that information in public? The case also raises the question of whether the Obama administration, which has brought more leak-related prosecutions than any previous administration, is overreaching in its desire to discourage leaks.

“There’s a real trade-off for the government, in which prosecuting may be more harmful to the nation’s interests than in not being able to prosecute,” said Geoffrey Stone, a University of Chicago constitutional law expert, referring to the balancing act between protecting classified information and a defendant’s right to a fair and open trial.

“The two goals are inherently in conflict,” said Barry J. Pollack, a lawyer defending a former CIA official, Jeffrey Sterling, in another leak-related prosecution. “A lot of these cases end up imploding because of that tension.”

The sudden collapse of the Drake case after years of preparation calls into question whether the Justice Department accurately assessed the likelihood of prevailing at trial, analysts said.

“It wasn’t a strong case to begin with,” said Steven Aftergood, a national security expert with the Federation of American Scientists. “Even the most basic facts, such as whether the documents in question were classified, were in dispute. So the government was beginning from a difficult position.”

The prosecution asked U.S. District Judge Richard Bennett to allow it to replace classified references with unclassified substitutions, but the judge said to do so would harm Drake’s ability to defend himself.

“These are tough cases by their very nature, but it is an important principle that people who have access to classified information follow the law and the agreements they signed to protect classified information,” said Laura Sweeney, a Justice Department spokeswoman. 

The Sterling case may illustrate other hurdles. The prosecution, led by Welch, is seeking to compel New York Times reporter James Risen to testify about his relationship with Sterling in order to establish Sterling was the source of classified information that appeared in his book.

“It seems they are unable to make their case without taking the extreme step of subpoenaing a reporter,” Aftergood said. “So the case is morphing into an assault on the press.”

The judge in that case has quashed one subpoena of the reporter. He is expected to oppose the government’s effort to force him to testify.

Sweeney said that in issuing subpoenas to reporters, the government “seeks to strike the proper balance between the public’s interest in the free dissemination of information and effective law enforcement.” She said Risen’s testimony “is directly relevant to facts that are squarely at issue in this trial.”

The outcome of the Drake prosecution has focused new attention on Welch, who headed the Justice Department’s Public Integrity Section when its corruption case against the late Sen. Ted Stevens (R-Alaska) collapsed. Welch was reassigned after Stevens’s 2008 conviction was tossed out, largely because of allegations of prosecutorial misconduct.

Senior department officials expressed confidence in Welch. “He is a person of really exceptional intellect,” said Assistant Attorney General Lanny A. Breuer, who heads the Justice Department’s criminal division and who put Welch in charge of the Drake and Sterling cases.

In the Drake case, Breuer said, Welch appropriately handled the challenge of balancing the need to protect NSA secrets and the desire for an open trial.

Pollack, who is opposing Welch in the Sterling case, agreed. “What happened in the Drake case could just as easily have happened if the prosecutor’s name were John Smith,” he said.

At the same time, Pollack said, the government pushed too hard.

“Anytime you set out to prove 10 felonies and you end up with one misdemeanor, you’ve overreached.”

Staff researcher Julie Tate contributed to this report.