"For safety reasons they terminated the flight," base spokesman Capt. Sean McKenna said.

The three-stage rocket was carrying a mock missile interceptor. It went off course about 30 seconds after launch.

The debris splashed into the Pacific Ocean about six miles from the base.

The mishap came after the booster's first test flight on Aug. 31 was declared successful.

Thursday's test did not involve any attempt to intercept a dummy warhead.

Eyewitnesses report seeing some kind of debris fall away from the Boeing-built missile just as it left its launch canister and fly into the exhaust plume. Something then appeared to stream off from the side of the first-stage motor.

The missile appeared to begin losing attitude control about 10 seconds into flight. It soon lost control and crashed into the Pacific Ocean.

The booster blasted out of an underground silo at 10:15 a.m., climbing into clear blue skies and leaving behind a lengthy white contrail as it cleared the ridge line. A hiccup in the climb was followed seconds later by the first of several small glowing red pieces falling back to Earth, in a dramatic display visible from vantage points around the Lompoc and Santa Maria valleys.

Cheers of "Go, baby!" gave way to whispers of "Uh, oh" as stunned onlookers stood silent at a Vandenberg hilltop that provided a clear vantage point as the pieces splashed into the ocean about a mile offshore.

The three-stage vehicle's pieces showered downward, as range safety crews issued commands to destroy the errant missile.

"They issued it 30 seconds into flight ... because it veered off course," said Capt. Sean McKenna, a Vandenberg spokesman.

Every rocket or missile that blasts off from Vandenberg carries special equipment that allows ground crews to blow up problem-plagued vehicles. Also, before launches the Air Force bans boats from the waters offshore as a safety precaution in case of an anomaly.

The $21 million booster verification test aimed to  prove a new missile using technology from other launchvehicles would work to carry the interceptors in the Pentagon's proposed Ground-based Midcourse System.

"Government and industry officials will conduct an investigation to see what the cause of the malfunction was," said Maj. Catherine A. Reardon, Ballistic Missile Defense Organization spokeswoman.

An Aug. 31 debut flight for this booster ended in success and officials had high hopes for the second test.