Washington

The Pentagon is planning new restrictions on the results of ballistic-missile defence tests — angering outside scientists who have until now monitored the tests and, on occasion, taken issue with the declared results.

Data from future tests involving target warheads and decoys will be classified as secret to prevent enemies from learning about the system's weaknesses, says Lieutenant Colonel Richard Lehner, a spokesman for the Missile Defense Agency. “You reach a point in a test programme where you have to start protecting the data,” he says.

The Pentagon has already tested aspects of its missile defence system, including its ability to differentiate ballistic missiles from decoys, but is planning a series of further tests.

From launch pad (bottom, inset) to impact (top) tests on interceptor missiles will soon be secret. Credit: MISSILE DEFENSE AGENCY

The secrecy argument holds little sway with researchers who have closely followed the development of the missile defence programme, such as Theodore Postol, professor of science, technology and international security at the Massachusetts Institute of Technology. “I think it's very clear why they're classifying information about the targets,” he says. “It's because they can't tell the difference between decoys and deployed warheads.”

Critics say that the Pentagon's move is an effort to deflect criticism from independent observers and Congress. They concede that the weapons system's vulnerabilities should be classified at some stage, but argue that the missile defence programme isn't close to the level of maturity to justify such classification.

“This programme is at a much earlier stage of development,” contends David Wright, a physicist at the Union of Concerned Scientists, a group based in Cambridge, Massachusetts, that has criticized the missile defence programme.

But Lehner says that the tests have reached a point of sophistication where providing details about its results will tip off potential adversaries about how the system works.

Phil Coyle, who directed the evaluation of missile defence during the Clinton administration and is now a senior adviser at the Washington-based Center for Defense Information, says that the Pentagon's move threatens to bury the whole programme in a cloud of secrecy. “If they classify their planning, the purposes of the tests and the results, it will be difficult for Congress and the public to know what's going on,” he says.

Lehner says that the programme will continue to share classified test information with the appropriate congressional committees, but not with the public. “We're not in a popularity contest,” he says. “We're trying to design a system that works.”

On 14 June, the Bush administration pulled out of the 1972 Anti-Ballistic Missile Treaty, clearing the way for a missile defence system. The next day, construction crews broke ground on the site at Fort Greeley, Alaska, that will be home to six interceptors. The Pentagon aims to provide what it terms “limited protection” from long-distance missile attack some time between 2004 and 2008.