A souped-up missile launched from a Navy ship successfully struck a dying and potentially deadly U.S. spy satellite passing 130 miles above the Pacific yesterday in a tricky operation that was almost scuttled due to rough seas.

The Pentagon said the USS Lake Erie, which is based at Pearl Harbor, fired a single modified tactical Standard Missile-3 at 5:36 p.m. Hawai'i time, hitting the satellite as it traveled in space at more than 17,000 mph.

For the best chance to succeed, the military had to wait for a combination of factors: steady seas around the Lake Erie, optimum positioning of the satellite as it passed in polar orbit, and the readiness of an array of space- and ground-based sensors to help cue the missile and track the results.

The operation was so extraordinary, with such intense international publicity and political ramifications, that Defense Secretary Robert Gates — not a military commander — made the final decision to pull the trigger.

A defense official last night said an initial view of the missile strike indicated it probably hit the spacecraft's fuel tank, whose toxic contents were the main target of the missile launch.

The aim was not just to hit the bus-sized satellite — which would burn up upon re-entering the atmosphere anyway — but to obliterate a tank on board that was carrying 1,000 pounds of hydrazine, a toxic fuel. The fuel, unused because the satellite died shortly after reaching orbit in December 2006 — could be hazardous if it landed in a populated area.

The Centers for Disease Control and Prevention issued a health bulletin saying that the health risk from satellite debris was considered to be low. "However, CDC is encouraging health officials and clinicians to review information about the health effects related to hydrazine to prepare in case their communities are affected by satellite debris."

Ray Lovell, a spokesman for Hawai'i Civil Defense, said his agency has been told the possibility of any debris coming down in the state was slight. Most of the debris should fall in a 24- to 48-hour period after the satellite was hit, Lovell said, although it may take a month for all of it to fall.

In preparation, the government organized hazardous materials teams, under the code name "Burnt Frost," to be flown to the site of any dangerous or otherwise sensitive debris that might land in the United States or elsewhere.

Also, six federal response groups positioned across the country by the Federal Emergency Management Agency were alerted but not activated, FEMA spokesman James McIntyre said. "These are purely precautionary and preparedness actions only," he said.

WEATHER FACTOR

High seas in the north Pacific posed the first obstacle as the USS Lake Erie prepared to launch a three-stage missile.

The plan was for the SM-3 to soar 130 miles to just beyond the edge of the Earth's atmosphere in an attempt to speed its nonexplosive warhead directly into the satellite.

Early in the day, a senior military officer said it didn't look as if the weather would be good enough. That was shortly after the space shuttle Atlantis landed at 4:07 a.m. Hawai'i time, removing the last safety issue for the military to begin determining the best moment for launch.

Another officer said hours later the weather was improving and might permit a launch. As a precaution, notifications were issued worldwide to mariners and aviators to stay clear of an area in the Pacific where satellite debris might fall. The military calculated that the risk to aviation was so low that U.S. and international aviation officials decided they would probably not reroute air traffic, a senior military officer said yesterday.

The officer briefed reporters at the Pentagon on technical and logistical matters related to the effort. Under ground rules set by the Pentagon, the officer could not be identified by name.

CLEAR INTENTIONS

The attempted shootdown, approved by President Bush, was seen by some as blurring the lines between defending against a hostile long-range missile and targeting satellites in orbit.

The U.S. had criticized China last year when China shot down one of its aging weather satellites in a test, leaving a debris field in a higher Earth orbit.

Shortly before the missile was launched, Adm. Mike Mullen, the chairman of the Joint Chiefs of Staff, met with service members at the officers club at Hickam Air Force Base on his way to Australia. He also addressed the planned shootdown.

Mullen said the U.S. has been open about its intentions with the failing satellite.

"Clearly, we're taking the shot at what we hope will be an altitude that minimizes the amount of space debris that will occur," he said.

He added that the U.S. had "engaged governments throughout the world to tell them what our intentions are."

"This is a system that is not designed for this kind of (satellite shootdown) capability," he said. "We actually had to modify the system in order to take this shot."

Much of the equipment used in the satellite shootdown was part of the Pentagon's missile defense system, a far-flung network of interceptors, radars and communications systems designed primarily to hit an incoming hostile ballistic missile fired at the United States by North Korea. The equipment, including the Navy missile, had never been used against a satellite or other such target.

IMPRESSIVE TESTS

The three-stage Navy missile, the SM-3, has chalked up a high rate of success in tests since 2002 — in each case targeting a short- or medium-range missile. A hurry-up program to adapt the missile for this anti-satellite mission was completed in a matter of weeks; Navy officials say the changes would be reversed once the satellite was down.

Gates was traveling to Hawai'i yesterday to kick off a nine-day trip. Officials said his stop at U.S. Pacific Command was scheduled before it was known that the satellite shootdown could happen while he was here.

Due to the relatively low altitude of the satellite at the time of the engagement, debris was expected to begin to re-enter the earth's atmosphere immediately.