``The launch has been postponed until tomorrow due to the poor weather conditions at Vandenberg Air Force Base'' in California, said Pentagon spokeswoman Cheryl Irwin.

The $100 million launch of a dummy warhead on a prototype Minuteman 2 booster rocket was originally scheduled for Saturday evening, but had to be postponed until Sunday due to high winds and low clouds.

Irwin said the launch would be attempted again between 9 p.m. EST Monday and 1 a.m. Tuesday.

``They would rather err on the side of caution when it comes to launches,'' Irwin said.

Air Force Lt. Col. Rick Lehner, a spokesman for the Pentagon's Ballistic Missile Defense Organization, said the dummy warhead carries sophisticated instruments to signal its location, but safety dictates that no launch may take place without clear skies for visual tracking of booster rockets. The test, often likened to a bullet trying to hit a bullet, is part of the Bush administration's goal of building a multi-layered shield to protect against ballistic missiles from nations such as North Korea, Iran and Iraq.

Monday's test would be the fifth intercept test. Two of the previous four tests failed.

Russia, China and other countries oppose U.S. efforts to develop a missile shield, saying it would violate arms control agreements and could lead to a renewed arms race.

In the test, a ``kill vehicle'' projectile fired from Kwajalein Atoll in the Pacific Ocean will attempt to destroy a dummy warhead launched from Vandenberg, about 4,800 miles away.

The kill vehicle must distinguish between the warhead and a decoy balloon and if all goes as planned would destroy the mock warhead about 144 miles above the sea from the sheer force of impact.

U.S. officials say the missile defense tests do not violate the 1972 Anti-Ballistic Missile Treaty between the United States and the former Soviet Union.

The White House has vowed to move beyond that pact if Moscow and Washington cannot reach agreement on updating it.

Despite agreeing to new and deep cuts in offensive nuclear missiles by both countries, Russian President Vladimir Putin and President Bush failed to agree on the anti-missile program at a summit meeting in Texas last month, but said discussions would continue.

Poor weather at Vandenberg Air Force Base, site of the planned launch of the target missile, forced the postponement until between 9 p.m. EST Sunday and 1 a.m. on Monday, ''contingent upon improvement of weather conditions,'' a statement said.

The launch of a dummy warhead on a prototype Minuteman 2 booster rocket had been scheduled to take place between 9 p.m. EST on Saturday and 1 a.m. on Sunday.

``The test was postponed because of high winds and low cloud cover'' at Vandenberg, on the central California coast, said Air Force Lt. Col. Rick Lehner, a spokesman for the Pentagon's Ballistic Missile Defense Organization.

Going into the test, the U.S. military had succeeded twice and failed twice in attempts to shoot down a dummy warhead fired from Vandenberg with an interceptor launched from Kwajalein Atoll in the Marshall Islands. The Bush administration's goal is to build a multi-layered shield to protect against feared ballistic missiles from nations such as North Korea, Iran and Iraq that could be tipped with chemical, biological or nuclear warheads.

Even though the dummy warhead carries sophisticated instruments to signal its location, safety dictates that no launch may take place without clear skies for visual tracking of booster rockets, Lehner said.

About 20 minutes after the target was to be launched from Vandenberg, an interceptor carrying a so-called ``kill vehicle'' would be fired from the Marshalls, about 4,800 miles (7,700 km) away.

If everything went according to plan, the kill vehicle would destroy the target by slamming into it 144 miles above the Pacific after they close on each other at a combined speed of about 15,000 miles per hour.

The anti-missile program put Washington at odds with Russia and China, which said it would lead to a new arms race.

ABM TREATY

The 1972 Anti-Ballistic Missile Treaty between the United States and the old Soviet Union barred both countries from building a national missile defense to curb their efforts to overwhelm any such shield.

While the test postponed on Saturday night would not violate the ABM treaty, the White House has vowed to move beyond that pact if Moscow and Washington cannot reach agreement on updating it.

U.S. Air Force Lt. Gen. Ronald Kadish, director of the Ballistic Missile Defense Organization, told reporters on Friday that he was ``pretty confident we fixed everything'' in the two failed intercept tries.

``But this is rocket science, so there is some chance that we missed something. That's why we're testing,'' Kadish said.

Despite agreeing to new and deep cuts in offensive nuclear missiles by both countries, Russian President Vladimir Putin and President Bush failed to agree on the anti-missile program at a summit meeting in Texas earlier this month.