NEW ORLEANS -- Federal prosecutors are asking a judge to disqualify a defense lawyer from representing two siblings of a Louisiana congressman in a fraud case, claiming the attorney has divided loyalties.

Ike Spears is defending New Orleans tax assessor Betty Jefferson and her brother Mose Jefferson -- siblings of U.S. Rep. William Jefferson, D-La. -- against charges they pocketed grant money earmarked for charitable and educational programs.

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Betty and Mose Jefferson

In court papers filed Monday, prosecutors argue that Spears shouldn't be allowed to represent the siblings because he also has represented a third member of the Jefferson family, who is cooperating with investigators.

U.S. District Judge Ivan Lemelle didn't immediately rule on the government's request to disqualify Spears from the case. Spears didn't immediately return a call for comment Tuesday evening.

Prosecutors said Spears provided legal counsel to Brenda Jefferson, the youngest Jefferson sibling, before she pleaded guilty in June to helping conceal the alleged fraud scheme in the charity case.

Spears shouldn't be allowed to cross-examine Brenda Jefferson if she testifies against her relatives because she isn't waiving her attorney-client privilege, prosecutors said.

"In short," prosecutors wrote, "Mr. Spears' loyalty is greatly divided, a status contrary to justice's demands of conflict-free resolution of a criminal proceeding."

Betty and Mose Jefferson and Angela Coleman, who is Betty's daughter, have pleaded not guilty to charges that include federal program fraud, identity theft and conspiracy to commit money laundering. William Jefferson is facing separate corruption charges over an alleged bribery scheme.

(Copyright 2008 by The Associated Press. All Rights Reserved.)