US missile defense plans are based on "technical myths" and interceptors have mostly failed to knock out incoming warheads in military tests, a new study argues.

Two American scientists reviewed 10 tests of the SM-3 "kill vehicle," designed to take out ballistic missiles, and concluded that the interceptor succeeded in directly hitting mock warheads in only one or two cases.

"This means that, in real combat, the warhead would have not been destroyed but would have continued toward the target and detonated in eight or nine of the 10 SM-3 experimental tests," wrote George Lewis of Cornell University and Theodore Postol of MIT in the latest issue of "Arms Control Today."

The Pentagon had described the tests between 2002 to 2009 as successful.

The US administration's claims about the missile defense system are "nothing more than a fiction" and "the policy strategy that follows from these technical myths could well lead to a foreign policy disaster," wrote the scientists in an article titled "A Flawed and Dangerous US Missile Defense Plan."

The authors also questioned if a network of early-warning satellites and radar could precisely track missiles and distinguish them from debris or decoys.

But the US Missile Defense Agency (MDA) on Tuesday rejected the findings of the study, calling them "flawed, inaccurate and misleading."

Defense Secretary Robert Gates retained confidence in the missile defense program, his press secretary told AFP.

"Secretary Gates tracks our missile defense program closely and he continues to have a high degree of confidence in its capabilities, including those of the SM-3 system," press secretary Geoff Morrell said in an email.

US officials and the authors of the study disagreed over the importance of the interceptors striking the body of a rocket or its dummy warhead.

The SM-3 tests "showed that the interceptor's kill vehicle impacted the target body or warhead within inches of the expected impact point that was calculated to maximize damage against a variety of warhead types," the MDA said in a statement.

MDA spokesman Richard Lehner said some of the earlier tests did not use mock warheads at all because the goal was merely to hit the target missile.

One of the authors of the study, Postol of the Massachusetts Institute of Technology, is a long-time skeptic of missile defense who previously helped expose the failure of most Patriot anti-missile weaponry in the 1991 Gulf War.

Much is riding on land and sea-based US missile defenses, with President Barack Obama arguing the system will help counter the threat posed by Iran's missiles and will allow for scaling back the American nuclear arsenal.