WASHINGTON (Reuters) - Military and industry experts began poring over test data on Wednesday to determine why the United States failed to hit a speeding missile warhead in a $100 million test of its planned national missile defense system.

The Defense Department said a hit-to-kill projectile fired from Kwajalein Atoll in the western Pacific did not smash into a dummy "enemy'' warhead launched from Vandenberg Air Force Base, California, 4,300 miles (6,900 kilometers) away on Tuesday night.

"An intercept was not achieved,'' the department said in a brief statement nearly two hours after the warhead lifted off on a Minuteman Missile at 9:19 p.m. Eastern time (0219 GMT Wednesday), followed 20 minutes later by firing of the anti-missile weapon.

There was no immediate announcement on prospects for a planned third test of the system, being integrated by Boeing Co., in April or May.

Tuesday's miss could affect a planned decision by President Bill Clinton this summer on whether to begin deploying a limited U.S. national missile defense based in Alaska at a cost of more than $12 billion, despite strong objections from Russia.

Clinton is under pressure from the Republican-led Congress to proceed quickly with a limited version of former President Ronald Reagan's "Star Wars'' national missile defesce program in order to protect U.S. cities against attack from rogue states such as North Korea.

But critics say the technology for such a defense is far from ready and that it is much too early to begin building a 100-interceptor base in Alaska.

"Government and industry program officials will conduct an extensive review of the test results to determine the reason(s) for not achieving an intercept and any other test objectives that were or were not met,'' the Defense Department said in a terse statement announcing the miss.

"It could take several weeks until the review is completed,'' the statement said.

While the kill vehicle hit the warhead at high speed during the less complicated test in October, the Pentagon conceded last week that there had been technical problems associated with that test that were not announced at the time.

"It's hard to hit a bullet with a bullet at closing speeds of 15,000 miles an hour (24,000 kph),'' Defense Department spokesman Ken Bacon told reporters before Tuesday's test, stressing the difficulty of the costly and yet unproven missile defense program.

Bacon, however, confirmed reports that the Pentagon planned to ask Congress soon to approve an additional $2.2 billion in spending on the missile defense plan, pushing the planned cost to at least $12.7 billion in the years ahead.

Tuesday's test was more difficult than last October's because it was to include and integrate the use of space- and ground-based radars in Hawaii and Kwajalein. Those radars, along with pinpoint global positioning systems, will become more important as the system evolves.

The test had international implications and was watched closely by governments as well as contractors involved. Boeing is the chief integrator and Raytheon builds the 121-pound (55-kilogram) weapon.

Russia has warned that a U.S. national missile defense system would violate the 1972 anti-ballistic missile treaty. Moscow has refused a U.S. request to modify the treaty to allow the system and cautioned that a go-ahead by Washington could threaten current nuclear arms reduction agreements.

But the White House and Pentagon stress that the limited system would in no way threaten to neutralize the nuclear arsenals of Russia or China.

Washington's European allies, meanwhile, have voiced concern that a successful U.S. defense against strategic missiles might isolate the world's only remaining superpower from its friends and cool America's military commitment to Europe.

The Pentagon currently plans a total of 19 intercept tests of the proposed national missile defense system. The system is now using prototype interceptors and rocket boosters because the final versions to be deployed will not be ready for testing until at least 2003.