Federal prosecutors pursuing the criminal case against former Democratic presidential candidate John Edwards today asked a judge in North Carolina to examine potential conflicts of interest involving Abbe Lowell, the high-powered attorney who heads Edwards’ legal team.

In particular, the government contends that Lowell’s prior representation of two likely prosecution witnesses could impact Edwards’ constitutional rights to conflict-free legal representation.

Edwards was charged in June in a six-count criminal indictment alleging that he participated in an illegal scheme to seclude and support his pregnant mistress, Rielle Hunter, while Edwards was seeking the 2008 Democratic nomination. The case centers on more than $900,000 from two wealthy donors: 101-year-old heiress Rachel Mellon and former Edwards’ campaign finance chairman Fred Baron, who died in late 2008. The government contends those payments were made in violation of federal election finance laws.

During the criminal investigation of Edwards’ campaign, Lowell represented Baron’s widow, Lisa Blue, and longtime Edwards’ pollster Harrison Hickman, who the government contends was among a small clutch of confidants that made decisions about how to respond to allegations about the affair. Both Hickman and Blue were interviewed by federal agents, and Blue was one of about a dozen witnesses who were called before the grand jury.

“Mr. Lowell’s prior relationship with Ms. Blue and Mr. Hickman certainly presents a real possibility that his cross-examination of them may not be as thorough as otherwise might be the case were an independent non-conflicted counsel conducting the examination,” the government said in a brief filed today.

Lowell joined Edwards’ defense team in July after another prominent attorney, former Obama White House counsel Greg Craig, withdrew. The government’s motion notes that the potential conflicts were discussed with Lowell prior to his official entry into the case.

According to the motion, Lowell contends there is no conflict because he no longer represents Hickman or Blue, and he is not in possession of any confidential information as a result of his prior relationships with them.

In a statement ABC News today, Lowell said, “We have discussed this issue with the government to its satisfaction; its inquiry to make a record is appropriate; and we will respond in a court filing.”

The government also notes that Lowell has denied ever having an attorney-client relationship with Fred Baron concerning the issues in this case, and that he told prosecutors he did not provide any advice to Baron or Blue about the filing of gift taxes.

But the government says in its motion that it has emails between Lowell and Rielle Hunter that appear to relate to “Mr. Lowell’s attempts to gather information from Ms. Hunter about monies Mr. Baron had given her and/or expenses of hers that Mr. Baron had paid in connection with the filing of gift tax returns for Mr. Baron.”

And though the government goes out of its way in the motion to make clear it is not accusing Lowell of improper conduct, the prosecutors raise the possibility that Lowell himself could become the subject of testimony because of his “potential conflicts.”

The government asks the judge to ensure that if Edwards waives his rights to conflict-free counsel, that the waiver is “knowing, intelligent, and voluntary.”

The government’s motion also details a previously undisclosed meeting at a hotel in late 2007, at which Elizabeth Edwards, in the presence of her husband, John Edwards, as well as Lisa Blue and Fred Baron, allegedly complained angrily that Baron and Blue had befriended Hunter and had been spending time with her. By that time, Hunter was pregnant, the National Enquirer was hot on the trail of the affair, and Edwards was still in a three-way race with Barack Obama and Hilary Clinton for the Democratic presidential nomination.

Edwards has pleaded not guilty to all the charges, and last month Lowell submitted a weighty barrage of motions seeking to dismiss the charges. Those motions will be addresses in a court hearing on Oct. 26.