Pentagon spokesmen refused to confirm or deny the report. But analysts said it was a virtual certainty that the defense system is working as a precaution and as an opportunity to test it against a real North Korean launch.

"It would only make sense, in that this is the missile that the system is designed to shoot down," said John Pike, director of GlobalSecurity.Org, a group that tracks military developments.

"I would say the probability that Kim Jong-il (the North Korean leader) is going to launch an attack on the United States is about as close to zero as anything gets in this world.

"But having spent all this time and motion on putting your missile defense system into place, you wouldn't want to get caught off guard."

"If he did launch an attack on America, and the missile defense system was on vacation that day, it wouldn't look good," he said.

Moreover, a North Korean test would be a golden opportunity to test the US system's ability to detect, track and target the missile and gather invaluable intelligence on the threat.

"This would be their first opportunity to actually get a look at what they were designed to kill," said Pike.

"And if the North Koreans are prepared to give us a full scale hardware-in-loop target practice well I'm sure sure they would like all of their sensors get a look a this thing."

Since the 1980s, the United States has spent nearly 90 billion dollars to come up with a system capable of protecting the United States and its deployed forces against missile attack, according to the Government Accountability Office, a Congress watchdog.

The current system is designed to defend against a limited missile strike by North Korea.

It currently consists of 11 ground-based missiles in silos -- nine at Fort Greely, Alaska and two at Vandenberg Air Force Base in California -- which are designed to intercept and destroy incoming long-range missiles in space.

If the system works as advertised, a North Korean missile launch would be detected by early warning satellites, picked up by US Aegis warships with modified Spy-1 radars and targeted with powerful radars in Alaska and California.

A giant new sea-based X-Band radar designed to detect, track and target warheads in space also might be put to work. A spokesman for the US Missile Defense Agency said it has been at sea in the Pacific for three weeks now.

Data received by those sensors would be relayed instantly to a command center in Colorado Springs, Colorado where computers would develop a targeting solution and cue interceptor missiles.

In tests, the system has had a mixed record even under conditions that critics say have been rigged for success.

The last successful long-range missile intercept test was in October 2002.

Of three tests since then, one failed in December 2002 because the interceptor's "kill vehicle" did not separate from the booster. In the next two tests in 2004 and 2005 the interceptor failed to launch.

The Washington Times said one option under consideration would be to use the system to shoot down the North Korean missile.

"We don't discuss any kind of alert status," said Pentagon press secretary Eric Ruff.

Pentagon officials, however, have said that because North Korean intentions are not known they would regard a North Korean missile shot as a "launch," rather than a "test."

The United States is unlikely to be able to tell from satellites whether the North Korean missile is armed or not, and will not know for sure it is a test until after it is launched, Pike said.

"Basically the only difference between firing this thing as a space launcher and firing it as an ICBM is payload and the trajectory that it follows once it has been launched," he said.

"After they have launched it, I think we would have a pretty good handle on what sort of trajectory it was flying within a couple of minutes," he said.

Japan, SKorea to cooperate to prevent NKorea missile test: report

Meanwhile, the foreign ministers of Japan and South Korea agreed Tuesday that their nations must cooperate to prevent North Korea from test-firing a long-range ballistic missile, a news report said.

The agreement came in a 25-minute telephone conversation late Tuesday between Japan's Taro Aso and his South Korean counterpart Ban Ki-moon, Japan's Kyodo news agency said, citing Japanese foreign ministry officials.

A series of reports have said North Korea is preparing to test-fire a Taepodong-2 missile with a range of up to 6,700 kilometres (4,200 miles), far enough to hit targets in Alaska and possibly Hawaii.

Japan and the United States have warned of a response to any launch, but South Korea has cautioned there is no certainty the Stalinist North is planning to conduct a test.

Aso and Ban expressed their deep concern over the current activities, the Japanese foreign ministry officials said, according to Kyodo.

Aso was quoted as telling Ban that it was important for concerned countries to cooperate in urging Pyongyang against a missile launch, which he called a threat to regional security.

Ban then agreed that such cooperation was needed, Kyodo said, relaying the comments of the Japanese foreign ministry officials.

North Korea caused alarm in August 1998 by firing a Taepodong-1 missile with a range of up to 2,000 kilometers over Japan into the Pacific Ocean. It later claimed it had succeeded in launching a satellite into orbit.

The North declared a moratorium on flight tests of long-range missiles in 1999 but said in 2005 that it would no longer observe it.

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