The latest flight test fizzled on Monday when an interceptor missile failed to launch from the Ronald Reagan Test Site on the Marshall Islands.

It was the second time in two months that an interceptor missile had failed to ignite, even as the target missile fired from Kodiak island, Alaska, arched unopposed over the Pacific.

The Missile Defense Agency said in a brief statement preliminary indications were that the problem lay with "ground support equipment, not the interceptor missile."

The previous test failure was blamed on a "very minor software glitch" that automatically shut down the interceptor missile moments before launch at an incoming target missile, officials said.

Analysts said the back-to-back failures appeared to reflect faulty engineering in a highly complex system rather than the technology that underpins missile defense.

But critics said that was all the more reason to be concerned about a hugely expensive program that has yet to prove that it can accurately track a warhead through space and distinguish it from decoys.

"Most of us thought that after Bush was elected in 2000 that by now we would have seen a half dozen intercept tests," said Joseph Cirincione, an expert at the Carnegie Endowment for International Peace.

"But they're having trouble getting these things out of the tubes. They are failing at a very basic level here. It should be a warning sign to everyone that this program is in deep, deep trouble, that it's time to pull back on the budgets, pull back on the scheduling," he said in an interview.

Annual missile defense spending peaked last year at close to 10 billion dollars under the Bush administration, which pressed to deploy by the end of 2004 a rudimentary system capable of defeating a limited intercontinental ballistic missile attack on the United States by North Korea.

That deadline came and went with no declaration that the system is operational. Missile defense officials insist an "emergency" capability is in place but have indicated there are no plans to declare it operational.

The last successful intercept occurred more than two years ago, raising questions about the system's viability.

"This is a Potemkin defense," said Cirincione. "It has shiny viewgraphs, it has big budgets, its has lots of generals, but there is no real defense there."

Cirincione said the program has advanced in some areas, such as boosters for the interceptors, guidance systems and miniaturization.

But other key areas such as decoy discrimination and tracking under realistic conditions have been left to later tests because it has yet to deploy powerful X-band targeting radars.

Missile defense officials have said they plan three more flight tests of the ground-based system this year, even as they expand the system.

Currently eight interceptors are in silos -- six at Fort Greely, Alaska and two at Vandenberg Air Force Base in California. Ten more more missiles are scheduled to go into silos in Alaska this year, and President George W. Bush proposed 2006 budget calls for procurement of 10 more this year.

However, with mounting deficits and growing costs of military operations in Iraq, the Pentagon this year proposed slashing the Missile Defense Agency's budget by a billion dollars this year and five billion dollars over six years.

Most of the cuts will be taken out of development of an even riskier effort to develop missiles capable of knocking down intercontinental missiles as they are boosting into space.

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