Blagojevich was found guilty on only one count, lying to the FBI, during his 2010 corruption trial. Jurors were deadlocked on the other 23. Prosecutors hope to simplify the case by dropping the three counts -- which include racketeering, racketeering conspiracy and wire fraud -- for the April retrial.
Blagojevich is accused of trying to sell or trade the U.S. Senate seat left vacant by U.S. President Barack Obama.
Judges rarely deny a request to drop charges from prosecutors, so Zagel's move was not a surprise.