United States Judge Stanley Sporkin could not believe what he was hearing, so he looked down once again at the Justice Department's top antitrust official and repeated the question: What if he could persuade Microsoft Corporation, which was trying to settle charges of unfair competition, to accept a few extra restrictions beyond those the Government had already negotiated? "Your honor," responded Anne K. Bingaman, the Assistant Attorney General for the antitrust division, "you don't have the power to do it." Scarcely containing his amazement, the judge tried again: "You mean to say, you wouldn't agree to it if they agreed to it?" "No," Ms. Bingaman replied, "I would not." It was a remarkable dialogue -- part of a long and heated hearing last month -- and it dramatized the bizarre predicament now confronting the Justice Department. Seven months after Ms. Bingaman boasted that her agency had forced mighty Microsoft to abandon its most unfair practices, she had in effect become its biggest ally.