A Department of the Treasury agency, stunned to discover that it has already given gun dealers permission to import more than 400,000 AK-47s and other assault rifles, ordered the Customs Service Friday to halt all shipments of the weapons at the nation's borders, the Los Angeles Times has learned.

The action goes far beyond steps taken two weeks ago, when the administration announced a temporary moratorium on newly issued permits for five types of assault weapons, including the AK-47 and Uzi carbine.The administration said at that time that it had no power to block shipments it had already approved. But an internal audit found that Treasury's Bureau of Alcohol, Tobacco and Firearms already had authorized imports of so many weapons that officials decided to take the emergency action.

Officials at the bureau refused to say how many assault weapons it had discovered already in the pipeline. A senior administration official, however, said that bureau officials had told him the number was 420,000.

Under the terms of the new order, the five types of weapons are now to be barred unconditionally from entering the United States.