The US military was waiting for the weather to clear up, however, as waves in the Pacific were too big for US warships to get in the right position to fire a missile at the bus-sized satellite, which is filled with toxic fuel.

"We don't anticipate the weather to be good enough," a senior military official said on condition of anonymity. "It has not been enough for us to say no but we are watching weather today."

The Pentagon's window of opportunity to shoot down the satellite opened Wednesday morning after the space shuttle Atlantis landed in Florida, clearing the skies for the navy to fire its missile.

The official said the window closes on February 29.

The plan drew criticism on Sunday from Russia, whose defense ministry said it looked like a veiled weapons test and an "attempt to move the arms race into space." China has also voiced concern.

Washington has denied seeking to cover up the satellite's technological secrets or to make a show of strength after China used a missile to shoot down an old weather satellite in January 2007.

Armed with two specially modified interceptor missiles, the USS Lake Erie cruiser has been tasked to intercept the satellite over the Pacific and shoot it down into the ocean, officials said Tuesday.

The USS Decatur, a guided missile destroyer, was carrying a third interceptor missile in case the first two attempts fail, defense officials said.

"I'm confident they'll be able to do something," a senior navy official said Tuesday. "Once the weapon goes into track, then I think it's a done deal."

The Pentagon is essentially employing the US missile defense system for the shoot-down attempt at an estimated cost of 40 to 60 million dollars.

It is training a panoply of Aegis warships, radars and computerized command networks on the school bus-sized satellite.

Software changes have been made to the SM-3 interceptor missiles so that they will recognize a satellite in space instead of a ballistic missile, the target they are normally programmed to destroy, officials said.

The three-stage missile will carry a maneuverable non-explosive warhead guided from the ground until it can use its infrared sensor to steer itself into a shattering collision with the satellite at an altitude of 150 nautical miles (278 kilometers).

US Navy ships have intercepted ballistic missile warheads in this way in tests, but the navy official, who briefed reporters on condition of anonymity, said the satellite poses a somewhat different problem.

It is colder and moving through space at a much higher speed, making it more difficult to track than the ballistic missiles.

If the USS Lake Erie misses with its first shot, it will probably have to wait a day to try again. The longer the wait, the harder the satellite will be to shoot down as it gathers speed, falling towards the Earth's atmosphere.

The plan is to hit a tank on the satellite carrying the toxic propellant hydrazine, which officials say could pose a threat to humans if it survives re-entry.

"The system itself is very accurate so hopefully that will translate into being able to hit the tank," said a defense official.

France urged the United States to take all necessary safety measures.

"We hope all measures will be taken to reduce as much as possible the consequences of destroying this satellite for the safety and integrity of other space objects," said foreign ministry spokeswoman Pascale Andreani.

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