President Bush ordered the action to prevent any possible contamination from the hazardous rocket fuel on board, and not out of any concern that parts of the spacecraft might survive and reveal its secrets, the officials said.

The military will try to shoot down a crippled spy satellite in the next two weeks, senior officials said Thursday. The officials laid out a high-tech plan to intercept the satellite over the Pacific just before it tumbles uncontrollably to Earth carrying toxic fuel, The effort will be a real-world test of the nation’s antiballistic missile systems and its anti-satellite abilities, even though the Pentagon said it was not using the effort to test its most exotic weapons or send a message to any adversaries. 

The ramifications of the operation are diplomatic, as well as military and scientific, in part because the United States criticized China last year when Beijing tested an anti-satellite system with an old weather satellite as a target

“This is all about trying to reduce the danger to human beings,” said James F. Jeffrey, deputy national security adviser.

The United States has opposed calls for a treaty limiting anti-satellite or other weapons in space. On Thursday, officials promised that the United States would remain wholly compliant with treaties requiring the notification to other nations before launching a missile at the disabled satellite.

The American military shot down a satellite in September 1985 in a test of an anti-satellite system under development. In that experiment, an F-15 Eagle fighter fired a missile.

Gen. James E. Cartwright of the Marines, vice chairman of the Joint Chiefs of Staff, said that if the first missile failed to strike the satellite, an assessment would be made within days and that two more missiles were ready. General Cartwright described little downside in trying to destroy the satellite.