Sources say MOAB ? still experimental ? is a 21,000-pound bomb that will be pushed out the back of a C-130 transport and guided by satellite. Because it is not dropped by parachute, as was the old Daisy Cutter, the aircraft can let it go from far higher altitudes, making it safer for U.S. pilots.

The MOAB's massive explosive punch, sources say, is similar to a small nuclear weapon.

Whatever the target, it must be far from cities where civilians might be hurt. But one important aspect of using this type of weapon, sources say, will be psychological impact on enemy troops. It is intended to terrorize Iraqi troops, drastically reducing their desire to continue the fight.