WASHINGTON >> Federal prosecutors, seeking to build a case against the WikiLeaks leader Julian Assange for his role in a huge dissemination of classified government documents, are looking for evidence of any collusion in his early contacts with an Army intelligence analyst suspected of leaking the information.

Justice Department officials are trying to find out whether Assange encouraged or even helped the analyst, Pfc. Bradley Manning, to extract classified military and State Department files from a government computer system. If he did so, they believe they could charge him as a conspirator in the leak, not just as a passive recipient of the documents who then published them.

Among materials that prosecutors are studying is an online chat log in which Manning is said to claim that he had been directly communicating with Assange using an encrypted Internet conferencing service as the soldier was downloading government files. Manning is also said to have claimed that Assange gave him access to a dedicated server for uploading some of them to WikiLeaks.

Adrian Lamo, an ex-hacker in whom Manning confided and who eventually turned him in, said Manning detailed those interactions in instant-message conversations with him.

He said the special server’s purpose was to allow Manning’s submissions to “be bumped to the top of the queue for review.” By Lamo’s account, Manning bragged about this “as evidence of his status as the high-profile source for WikiLeaks.”

Wired magazine has published excerpts from logs of online chats between Lamo and Manning. But the sections in which Manning is said to detail contacts with Assange are not among them. Lamo described them from memory in an interview with The New York Times but said he could not provide the full chat transcript because the FBI had taken his hard drive, on which it was saved.

Since WikiLeaks began making public large caches of classified U.S. government documents this year, Justice Department officials have been struggling to come up with a way to charge Assange with a crime. Among other things, they have studied several statutes that criminalize the dissemination of restricted information under certain circumstances, including the Espionage Act of 1917 and the Computer Fraud and Abuse Act of 1986.

But while prosecutors have used such laws to go after leakers and hackers, they have never successfully prosecuted recipients of leaked information for passing it on to others — an activity that can fall under the First Amendment’s strong protections of speech and press freedoms.

Last week, Attorney General Eric H. Holder Jr. said he had just authorized investigators to take “significant” steps, declining to specify them. This week, one of Assange’s lawyers in Britain said the attorneys had “heard from Swedish authorities there has been a secretly impaneled grand jury” in Northern Virginia.

Justice Department officials have declined to discuss any grand jury activity. But in interviews, people familiar with the case said the department appeared to be attracted to the possibility of prosecuting Assange as a co-conspirator to the leaking because it is under intense pressure to make an example of him as a deterrent to further mass leaking of electronic documents over the Internet.

By bringing a case against Assange as a conspirator to Manning’s leak, the government would not have to confront awkward questions about why it was not also prosecuting traditional news organizations or investigative journalists who also disclosed information the government said should be kept secret — including The Times, which also published some documents originally obtained by WikiLeaks.

“I suspect there is a real desire on the part of the government to avoid pursuing the publication aspect if it can pursue the leak aspect,” said Daniel C. Richman, a Columbia law professor and former federal prosecutor. “It would be so much neater and raise fewer constitutional issues.”

It has been known that investigators were looking for evidence that one or more people in Boston served as an intermediary between Manning and WikiLeaks, taking a disc of files he had copied from a computer while deployed in Iraq and somehow delivering it to the website.

But Lamo said Manning also sometimes uploaded information directly to Assange, whom he had initially sought out online. The soldier sent a “test leak” of a single State Department cable from Iceland to see if Assange and WikiLeaks were who they claimed to be, Lamo said.

“At some point, he became satisfied that he was actually talking to Assange and not some unknown third party posing as Assange, and based on that he began sending in smaller amounts of data from his computer,” Lamo said. “Because of the nature of his Internet connection, he wasn’t able to send large data files easily. He was using a satellite connection, so he was limited until he did an actual physical drop-off when he was back in the United States in January of this year.”

Still, prosecutors would most likely need more than a chat transcript laying out such claims to implicate Assange, Richman said. Even if prosecutors could prove that it was Manning writing the messages to Lamo, a court might deem the whole discussion as inadmissible hearsay evidence.

Prosecutors could overcome that hurdle if they obtained other evidence about any early contacts — especially if they could persuade Manning to testify against Assange. But two members of a support network set up to raise money for his legal defense, Jeff Paterson and David House, said Manning had declined to cooperate with investigators since his arrest in May.

Meanwhile, WikiLeaks is taking steps to distance itself from the suggestion that it actively encourages people to send in classified material. It has changed how it describes itself on its submissions page.

“WikiLeaks accepts a range of material, but we do not solicit it,” its website now says.

It also deleted the word “classified” from a description of the kinds of material it accepts. And it dropped an assertion that “Submitting confidential material to WikiLeaks is safe, easy and protected by law,” now saying instead: “Submitting documents to our journalists is protected by law in better democracies.”

WikiLeaks is also taking steps to position itself more squarely as a news organization, which would make it easier to invoke the First Amendment as a shield. Where its old submissions page made few references to journalism, it now uses “journalist” and forms of the word “news” 23 times.

Another new sentence portrays its primary work as filtering and analyzing documents, not just posting them raw. It says its “journalists write news stories based on the material, and then provide a link to the supporting documentation to prove our stories are true.”