WASHINGTON — Army investigators are broadening their inquiry into the recent disclosure of classified military information to include friends and associates who may have helped the person they suspect was the leaker, Pfc. Bradley Manning, people with knowledge of the investigation said Friday.

Two civilians interviewed in recent weeks by the Army’s criminal division said that investigators were focusing in part on a group of Manning’s friends and acquaintances in Cambridge, Mass. Investigators, the civilians said, apparently believed that the friends, who include students from the Massachusetts Institute of Technology and Boston University, might have connections to WikiLeaks, which made the documents public.

It is unclear whether the investigators have specific evidence or are simply trying to determine whether one person working alone could have downloaded and disseminated tens of thousands of documents.

The Army has charged Manning with disclosing a classified video of a U.S. helicopter attack to WikiLeaks, as well as more than 150,000 classified diplomatic cables. Military officials said Friday that the private was also the main suspect in the disclosure to WikiLeaks of more than 90,000 classified documents about the Afghan war, some of which were published this week by The New York Times, the German magazine Der Spiegel and the British newspaper The Guardian.

A military official acknowledged Friday that Army investigators were looking into whether Manning physically handed compact discs containing classified information to someone in the United States. Manning, an intelligence analyst who was deployed over the past year in Iraq with the 2nd Brigade of the 10th Mountain Division at a remote base east of Baghdad, visited friends in Boston during a home leave in January.

Investigators believe that he exploited a loophole in Defense Department security to copy thousands of files onto compact discs over a six-month period. In at least one instance, according to people familiar with the inquiry, Manning smuggled highly classified data out of his intelligence unit on a disc made to look like a music CD by Lady Gaga.

Adrian Lamo, a computer hacker who this year traded instant messages with Manning, said in a telephone interview Friday that he believed that WikiLeaks was in part directing Manning and providing technical assistance to him in downloading classified information from military computers. Military officials would not confirm Lamo’s claim. Julian Assange, the founder of WikiLeaks, did not respond to an e-mail seeking comment.

Lamo, who turned Manning in to the authorities, is cooperating with the Army and has a strained relationship with WikiLeaks. Last month, WikiLeaks denounced Lamo, along with a Wired News reporter, Kevin Poulsen, who broke the story about Manning’s arrest, as "notorious felons, informers and manipulators."

As Lamo characterized it in Friday’s interview, Manning "was to a great extent manipulated by WikiLeaks." Lamo, who had extensive e-mail exchanges with Manning before reaching out to the authorities, said he believed that "there is at least one co-conspirator but probably more."

Lamo said that he believed that a person with ties to WikiLeaks had helped Manning set up encryption software that would have allowed him to e-mail small bits of classified data outside the military computer system without detection. According to Lamo, the small bits were meant to attract the notice of Assange.

Lamo acknowledged that he had no direct evidence that Manning had help. He said he based his belief on information from people who knew Manning, not on his contact with the soldier himself. Asked if Manning had ever told him of any WikiLeaks assistance, Lamo replied, "Not explicitly, no."

In one e-mail that Manning sent to Lamo in May, the private described his role with WikiLeaks as "a source, not quite a volunteer."

One of the civilians interviewed by the Army’s criminal division, who asked for anonymity so that his name would not be associated with the inquiry, said Friday that the investigators’ questions led him to believe that the Army was concerned that there were classified documents in the Boston area.

"I was under the impression that they believed that perhaps Bradley had used friends in Cambridge as a mechanism for moving documents," he said.

The civilian also said that the Army had offered him "a considerable amount of money if I were to keep my ear to the ground and be an in with them with WikiLeaks." He said that he had turned the Army down and that he had no connection to WikiLeaks. The other civilian also said in an interview Friday that he had no connection to WikiLeaks.

The first civilian said it appeared from the questioning that Army investigators "are trying to build a network among Bradley’s friends to infiltrate WikiLeaks."

Defense Secretary Robert M. Gates denounced WikiLeaks on Thursday for endangering lives because it included the names and villages of Afghan informants in the documents released. He has asked the FBI to assist in the Army inquiry. Unlike the military, the FBI can prosecute civilians.

The Times, and the two other publications given access to the documents, posted online only selected examples from documents that had been redacted to eliminate names and other information that could be used to identify people at risk.