WASHINGTON -- Pentagon officials next month will put a futuristic -- and highly controversial -- missile-defense system to its toughest test yet in the skies over the Pacific Ocean.

For the first time, the July 7 test of the National Missile Defense (NMD) system will include in-flight communications between ground controllers and a "kill vehicle" to track the device on its way toward an incoming target missile.

Now, ground controllers will have two opportunities to "talk" to it while it's racing to hit the target during the 30-minute test.

"Our objectives are basically the same as the previous two flight tests, but this is the first with an integrated communications system," Air Force Lt. Gen. Ronald Kadish, head of the Ballistic Missile Defense Organization said Tuesday.

"We want all those elements to work togetherso we can accomplish the intercept," he said.

As in the other tests, the July 7 demonstration will feature a modified Minuteman 2 that is launched westward from Vandenberg Air Force Base, California with a 5-foot- (1.5-meter-) long dummy warhead.

Twenty minutes later, an interceptor missile with a prototype kill vehicle will be launched from Kwajalein Atoll in the Pacific Ocean, about 4,000 miles (6,435 kilometers) away.

The kill vehicle is to chase the target warhead for about 10 minutes, using sensitive heat-seeking instruments to locate it in space about 144 miles (230 kilometers) above the ocean. Then, the kill vehicle is designed to slam into the target with a closing speed of 4.6 miles (7.5 kilometers) a second, instantly vaporizing both vehicles.

The time of the launch window for the July test is about four hours, starting at 9 p.m. Eastern Daylight Time (July 8, 01:00 GMT).

The first flight-test, last October, succeeded. The second, in January, failed when the kill vehicle missed the target due to a last-second failure in a cooling line in one of the vehicle's heat-seeking sensors.

The upcoming $100 million test has been delayed twice as a result of two months' additional work on the kill vehicle after the January failure.two successful intercepts in advance of its recommendation this summer to President Clinton on whether or not he should order the system's deployment. By law, the U.S. must develop the NMD system when it is technically feasible to do so.

The goal is to guard against missile attacks from rogue nations by having 20 missile interceptors in place by 2005. That's when the CIA estimates that North Korea will be ready to deploy long-range ballistic missiles capable of hitting the United States.

In order to make the 2005 deadline, a decision must come this year to proceed with construction of a giant radar facility on Shemya Island in the Aleutian chain.

An additional 80 interceptors would be in operation by 2007. The Pentagon estimates that a 100-interceptor system would cost $36 billion over a 20-year lifetime.

At least 16 more intercept tests are planned by 2005 -- with eight of them to take place before 2003. That's the year when a presidential decision would have to be made on whether to build the interceptor missiles for operational use.

Critics -- including prominent physicists and weapons experts from around the country -- have questioned the system as being technically flawed and tested under unrealistic conditions to get a passing grade.

Deployment of such a system, the critics warn, would violate the 1972 Anti-Ballistic Missile (ABM) Treaty designed to curb the spread of intercontinental ballistic missiles (ICBMs). It also could aggravate U.S. relations with both Russia and China, both of which oppose the NMD.

A recent report by a review panel headed by retired Gen. Larry Welch, former chief of staff of the Air Force, gave missile-defense developers a "B-plus grade" for work so far. But the report noted that there were engineering problems in the interceptor missile.

Developmental problems are to be expected with such a cutting-edge system, said Jacques Gansler, the Pentagon's technology chief.

"This is a whole new domain for us," he said. "We haven't been shooting down ICBMs recently."

But nothing has cropped up in the technology that could derail such a system, Kadish said. "This is not easy. But nothing we see today says we can't do this."