The new lawyers for John O’Brien, the disgraced former head of the state Probation Department, denied speculation Thursday that he is cooperating with authorities and strongly asserted that he will challenge the federal case against him at trial.

“There’s been a lot of recent suggestion that Mr. O’Brien is or has cooperated with the government,” said Stylianus Sinnis, who was appointed along with William W. Fick to represent O’Brien in a federal racketeering case.

“He looks forward to trying the case, and we firmly believe that the trial will demonstrate that nothing he did was criminal,” Sinnis added.

O’Brien and two former deputies, Elizabeth V. Tavares and William H. Burke III, face lengthy prison terms if convicted on charges that they rigged a hiring process in the Probation Department to benefit themselves and legislators who funded their budget.

O’Brien also faces a state bribery case that alleges that he organized a fund-raiser for Timothy P. ­Cahill, then state treasurer, to help his wife, Laurie O’Brien, get a job at the state lottery, which was under Cahill’s control.

‘He looks forward to trying the case. We firmly believe that the trial will demonstrate that nothing he did was criminal.’

There has been much speculation that witnesses and possibly even defendants in the case have or might cooperate with authorities. That speculation followed the public disclosure two weeks ago during a hearing in the state case that two of O’Brien’s former top aides have been granted immunity from prosecution, in exchange for their cooperation in the state and federal investigations.

Legal analysts suspected that prosecutors would even try to make a deal with O’Brien in exchange for testimony against politicians who benefited from the system. No politician has been indicted in the year-plus investigation, though officials have maintained that the probe is ongoing.

Sinnis sought to make clear Thursday that O’Brien has not cooperated.

At a brief hearing on the federal charges Thursday, he also indicated that he may seek to have a protective order lifted that limits the release of information in the case, as he begins to explore the charges against his client.

Bradford Bailey, a lawyer for Tavares, said he might join the request.

The request to lift the order was put on hold as prosecutors said they plan to turn over thousands of additional pages of discovery to the defense.

Also Thursday, John Amabile, a lawyer for Burke, questioned whether federal prosecutors would turn over information about witnesses who have been granted immunity.

Assistant US Attorney Fred M. Wyshak Jr. indicated, however, that he would not disclose such information until necessary and appropriate, saying the information was needlessly released at the state level and released to the media. As a result, he said, one of the witnesses whose cooperation was made public has been harassed by co-workers.

The case was continued to Sept. 20.