The US military does not anticipate trying to shoot apart a defunct spy satellite on Thursday due to rough seas in the Pacific Ocean, a senior military official said.
The official said that assessment could change but forecasts indicated the Pacific would not be calm enough for the operation. Under the Pentagon's plans, a Navy ship will fire a missile at the bus-sized satellite.
"We don't anticipate the weather being good enough today," said the official, briefing reporters at the Pentagon on condition of anonymity.
The Pentagon said last week that President George Bush had decided the Navy should try to shoot down the satellite because its fuel tank could leak deadly toxic gas if it enters the atmosphere and reaches Earth.
Officials had said they would start looking for opportunities to shoot at the satellite after the space shuttle Atlantis ended its latest mission. The shuttle touched down in Florida at 9:07am EST (3:07am NZT).
The senior military official said the window for striking the satellite would last until around the end of this month, when the vehicle enters the Earth's atmosphere.
"We'll make decisions each day as to whether we're going to proceed or not," the official said.
The official said the operation would likely take place during daylight in the Pacific.
The satellite is a National Reconnaissance Office spacecraft launched in December 2006 that stopped communicating within a few hours of reaching orbit, the Pentagon has said.
Russia and China have both expressed concern about the operation. The Russian Defense Ministry said it could be used as cover to test a new space weapon.
Washington has insisted the operation is purely to prevent people being harmed by the satellite's fuel tank, which contains the chemical hydrazine, if it falls to Earth intact.
"We've been very clear about why the president made this decision," Pentagon spokesman Bryan Whitman said. "This is about reducing risk to human life on Earth."
The United States has strongly criticized China for firing a ground-based missile into an obsolete Chinese weather satellite in January 2007.
Neither Washington nor Moscow has conducted an anti-satellite operation since the 1980s.