The Justice Department will ask a federal judge in Detroit to dismiss the convictions of three men in a high-profile terrorism case last year, saying it has uncovered serious prosecutorial misconduct in the case.

Department lawyers have told U.S. District Judge Gerald Rosen and defense attorneys that the convictions should be thrown out because prosecutors failed to share potentially exculpatory evidence with the defense during last year's trial, legal sources said last night.

The convictions of two Moroccan immigrants for conspiracy to provide material support for terrorism and of a third man on document fraud charges represented one of the government's most significant victories in the war on terrorism in the aftermath of the Sept. 11, 2001, attacks.

The move to vacate the convictions comes in the midst of the Republican National Convention, where President Bush is highlighting his success in the war on terrorism as the centerpiece of his reelection campaign.

Rosen and the Justice Department have been investigating allegations that two assistant U.S. attorneys withheld information from the defense. The department is continuing an investigation of one of the prosecutors, Assistant U.S. Attorney Richard Convertino, who has responded by suing the government. He alleges that Justice undermined the prosecution and sought to make him the scapegoat.

William Sullivan, Convertino's attorney, declined to comment yesterday, citing a gag order in the case. Other lawyers in the case also cited the order.

A filing from the Justice Department is expected as early as today seeking to have the convictions overturned and detailing the alleged misconduct. The department is expected to say that it will not seek reinstatement of the terrorism-related charges against defendants Karim Koubriti and Abdel-Ilah Elmardoudi but will seek to retry them and a third man, Ahmed Hannan, on document fraud charges.

Details of the government's request to vacate the convictions were first reported on U.S. News & World Report's Web site last night.

In the first terrorism-related trial since the Sept. 11 attacks, Elmardoudi, 37, of Minneapolis, and Koubriti, 26, of Detroit, were convicted in June 2003 of conspiring to provide material support to terrorists and document fraud. Hannan, 35, of Detroit was convicted of document fraud, and Farouk Ali-Haimoud, 22, of Detroit was cleared of all charges.

Justice Department officials, including Attorney General John D. Ashcroft, asserted the men were in a sleeper cell associated with al Qaeda and had plans to secure weapons and attack targets in the United States and abroad.

Authorities stumbled on some of the men when they raided a Detroit apartment shortly after the Sept. 11 attacks in a search for Nabil al-Marabh, who was on a terrorist watch list. They later termed the apprehension one of the most significant in the United States in the war against terrorism.

Throughout the trial, defense attorneys accused the prosecution of withholding key information and witnesses. Convertino admitted that prosecutors should have turned over information earlier but said it was not relevant. Rosen chastised Convertino in open court and said that was not his decision.

Rosen ordered a full review of the information available to the government. Last September, then-Detroit U.S. Attorney Jeffrey Collins removed Convertino and another assistant U.S. attorney, Keith Corbett, from the case, asking the Justice Department to investigate their handling of it.

Rosen also issued a rare rebuke of Ashcroft for exhibiting "a distressing lack of care" in public statements about the case.

In February, Ashcroft took the rare step of appointing a "special attorney," Craig S. Morford, to investigate the prosecutors' conduct. The same month, Convertino filed a lawsuit against Ashcroft and the Justice Department, alleging that he was the target of a smear campaign that resulted in the unmasking of a valuable informant.

Convertino alleged that the terrorism cases were undermined by "gross mismanagement" and a "lack of support and cooperation, lack of effective assistance, lack of resources and intradepartmental infighting."

A legal source familiar with the case said yesterday that the government also failed to turn over a photo it had of the route to a facility overseas that it considered the target of a potential terrorism attack. The source said the photo did not match a sketch it had introduced at trial.

The source said the government also withheld from the defense an interview with a retired CIA agent whose testimony was not as strong as the government had hoped.

One piece of information withheld from the defense was a December 2001 letter, obtained by prosecutors, from a convicted drug dealer who wrote that a key prosecution witness, Youssef Hmimssa, told him while they were in jail together "how he lied to the FBI, how he fool'd the Secret Service agent on his case."

Equally significant, one defense lawyer said, was an FBI interview with a former roommate of two defendants who said the men never talked about religion, were lazy, and often drank and smoked. That was in direct contrast to the picture painted by Convertino, who said they were devout Muslims.