WASHINGTON — The U.S. military likely will make its first effort to shoot down a crippled U.S. spy satellite that's approaching Earth's atmosphere sometime after 4:30 p.m. Hawai'i time today, the Pentagon announced yesterday, in what will be a major test of America's anti-ballistic missile program.

The Pearl Harbor-based USS Lake Erie, a Ticonderoga class missile cruiser with an Aegis weapons system, will launch an SM-3 tactical missile toward the satellite from somewhere west of the Islands, the Pentagon said. If that missile misses, the Navy has two other missiles on standby to launch, most likely tomorrow or Friday, the Pentagon said.

A Federal Aviation Administration advisory warned airlines that the launch could happen between 4:30 and 7:30 p.m. Hawai'i time.

U.S. officials announced last week that the Navy will try to down the satellite out of concern that a tank carrying 1,000 pounds of hydrazine, an ammonia-like chemical used in rocket fuel, might survive re-entry into the atmosphere and land in a populated area. Hydrazine can be toxic if swallowed or inhaled.

The plan, however, is controversial. Some experts have suggested that the attempt is really an effort to expand the capabilities of the anti-ballistic missile system to include satellites and to publicly counter China's demonstration destruction of an aged weather satellite last year. The United States denounced that Chinese test.

The missile and the roughly 5,000-pound spy satellite, which failed shortly after it was launched in December 2006, will close in on each other at roughly 20,250 mph, officials said.

The shoot-down isn't a sure thing. The missiles that will be used were designed to bring down ballistic missiles, and their software had to be rewritten to target the satellite, which moves faster than a ballistic missile.

The missiles also will find tracking the satellite difficult because, without power, it will be cooler than a ballistic missile. A senior Navy official, who couldn't be quoted by name under Pentagon press rules, said that the timing of the shoot-down was chosen partly so that the afternoon sun over the Pacific would warm the satellite, making it more likely that the missile will find it 150 miles above the Earth's surface.