Prosecutors have signaled no interest in giving Mr. Snowden credit for the surveillance debate he started.

“He is accused of leaking classified information, and there is no question his actions have inflicted serious harms on our national security,” said Marc Raimondi, a Justice Department spokesman. He said Mr. Snowden was not a whistle-blower.

Any deal could depend on what information Mr. Snowden could give in return.

In December, Richard Ledgett, who was then the National Security Agency official leading the response to the leaks and has since become the agency’s deputy director, floated the idea of a deal in which Mr. Snowden would receive leniency in exchange for returning documents in his possession that he had not disclosed.

“I would need assurances that the remainder of the data could be secured, and my bar for those assurances would be very high,” he said. “It would be more than just an assertion on his part.”

It is not clear whether Mr. Ledgett was suggesting an outcome in which Mr. Snowden persuaded journalists to destroy or return the documents, or whether the government believed Mr. Snowden had kept back documents to use as leverage.

Mr. Snowden has repeatedly said he did not bring any documents to Russia. He recently told Vanity Fair that there was no “doomsday cache” in his possession, saying, “Who would set up a system that incentivizes others to kill them?”

Even if he has no documents to return, Mr. Snowden could also help the N.S.A. by providing an accounting of what he took. Despite government claims that Mr. Snowden may have taken 1.7 million documents, Mr. Snowden also told Vanity Fair that figure is “a scare number based on an intentionally crude metric: everything that I ever digitally interacted with in my career.”