The 85-million-dollar test "could result in an intercept," but that is not the objective, said Rick Lehner, a spokesman for the agency.

"The idea is to collect as much targeting data as possible," he said in an interview.

This test will pave the way for a full-fledged attempted interception in March or April, he said. That test will incorporate an Aegis destroyer as a forward radar for the first time, he said.

In earlier tests, target missiles have been successfully intercepted in five of eight attempts. But since the last test in December 2002, flight tests have been delayed or cancelled six times, adding to questions about the viability of the system.

Despite the lack of recent flight tests, President George W. Bush is expected to declare the system operational by the end of this year.

The first four-hour window for the latest test is scheduled to open at 9:00 pm Wednesday, but if this window is missed there will be other opportunities through December 12, officials said.

If all goes according to plan, a modified Polaris target missile will be fired from a new test site at Kodiak Island, Alaska.

Within minutes, an interceptor missile will be launched into its path from Kwajalein atoll in the Marshall Islands.

Lehner said the test will be over in 30 minutes.

It will feature a new booster that is 20 to 30 percent faster than the modified Minuteman II missile used to power the interceptor into space in previous tests.

"It's the first time it's been used going up against a missile in an integrated flight test," said Lehner.

Atop the booster is a "kill vehicle," a 70-kilogram (155-pound) contraption with infrared and optical sensors to seek out and identify a warhead in space. It uses small jets to steer itself into a collision with the warhead.

Lehner said the kill vehicle used in this test has a number of modifications and improvements since the last test in December 2002.

"It's really in an operational configuration so we want to see how well it collects data," he said.

But the test will rely on simulated rather than actual radar data from two key elements of the system - an upgraded Cobra Dane early warning radar on Shemya Island in Alaska Aleutian chain, and an Aegis destroyer in Hawaii.

Lehner said the simulated tracking data will be fed into the Aegis destroyer's fire control system during the test.

In an actual operation, the destroyer would be positioned as close as possible to the source of the hostile missile launch. Its Spy-1 phased array radar could then be used to track the missile in the early phases of its trajectory when it releases it warhead.

The Cobra Dane radar also would track the warhead, relaying data to command centers in the United States which would then use it to launch the interceptor missile into its path.

Lehner said the Cobra Dane radar was not being used because its location is unsuited for the test.

Using Kodiak Island as a launch site, on the other hand, offers the opportunity to test the system against missiles traveling on new and somewhat more realistic trajectories.

In previous tests, target missiles were fired from Vandenberg, California over the Pacific, the opposite direction from which a missile attack on the United States would likely come.

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