President Bush made the decision because it was impossible to predict where a tank containing the fuel might land in an uncontrolled descent, officials said.  The Pentagon said it decided to use a modified, ship-fired anti-ballistic missile to make the attempt sometime after Feb. 20 to avoid creating debris that could threaten the space shuttle on its return from the international space station.  Marine Gen. James E. Cartwright, the vice chairman of the Joint Chiefs of Staff, said the Navy missile will be fired as the satellite reenters the atmosphere and "has a reasonably high opportunity for success." The Pentagon and NASA have been working on the missile modifications for the past three weeks.  Deputy national security adviser James F. Jeffrey said the decision was based on the fact that the satellite is carrying a substantial amount of hydrazine, a hazardous rocket fuel.  When the pending crash was first announced last month, however, National Security Council spokesman Gordon Johndroe and other officials minimized the danger, saying that the potential for harm was "very small."  Unless it is shot down, the satellite, which has been out of ground communication since its launch more than a year ago, is expected "to make an uncontrolled reentry . . . on or about March 6," according to documents the Bush administration provided to the United Nations yesterday. "At present," said an official notification sent yesterday to countries around the world as well as to the United Nations and NATO, "we cannot predict the entry impact area."  Officials acknowledged yesterday that many satellites and spacecraft parts -- some of them much larger -- have fallen to Earth in the past without causing harm. But they said the presence of 1,000 pounds of hydrazine -- unexpended fuel contained in a 40-inch sphere that was likely to hit the ground intact -- led Bush to approve the shoot-down.  The announcement set off an immediate debate on defense blogs and among experts who questioned whether there is an ulterior motive. Some experts said the military is seizing an opportunity to test its controversial missile defense system against a satellite target.  But others noted that the Standard Missile-3 has successfully been tested against warhead targets, which are far smaller than the satellite.  "There has to be another reason behind this," said Michael Krepon, co-founder of the Henry L. Stimson Center, a liberal arms-control advocacy organization. "In the history of the space age, there has not been a single human being who has been harmed by man-made objects falling from space."  NASA Administrator Michael D. Griffin insisted that the interception attempt is not a ruse to try the defense system on a satellite or to one-up countries that have made similar attempts. The administration was harshly critical of China when it destroyed an aging satellite in orbit a year ago.
A Navy cruiser in the Pacific Ocean will try an unprecedented shoot-down of an out-of-control, school-bus-size U.S. spy satellite loaded with a toxic fuel as it begins its plunge to Earth, national security officials said yesterday.