A space experiment that showed it would be easier than previously thought to distinguish Soviet nuclear warheads from decoys made it possible to cut the estimated cost of first phase "Star Wars" deployment nearly in half, a deputy program director says.

Brig. Gen. Garry Schnelzer, in an interview last week, told United Press International that a Feb. 8 Delta 181 rocket experiment from Cape Canaveral "gave us insight into how the optical sensors and radars would work together to discriminate between warheads and decoys."The deputy director for systems of the Strategic Defense Initiative, or "Star Wars," said the experiment was "extremely important" because it provided experts with information on how a number of differently shaped objects would appear in space to "those sensors we would use in midcourse intercept."

On Oct. 6, a panel of senior defense officials approved a plan that would cut the projected cost of a first phase deployment from $115 billion to $69 billion by halving the planned number of rocket-firing space platforms, designed to intercept missiles shortly after launch, from 300 to 150.

To compensate, the number of ground-based interceptors designed to destroy warheads after they have been launched into orbit was increased from the originally planned 1,000 to 1,700.

The change has placed greater stress on the mid-course intercept of missiles after they have placed their warheads in orbit as opposed to a "boost phase" intercept shortly after launch. Each missile can carry up to 10 warheads.

But space expert John Pike of the Federation of American Scientists said another change - the reduction in the number of satellites used to discriminate warheads from decoys from 80 to 20 - has significantly lessened SDI's midcourse intercept capability.

"These cuts significantly lessen the ability of a U.S. space defense to separate Soviet decoys from nuclear warheads at a time when the Soviet threat is likely to become more dangerous," Pike told UPI.

Each of the 20 space surveillance and tracking satellites (SSTS) also would be less capable because the "aperture" or opening of their telescope "sensors" would be about half that originally planned, Pike said.

The cut in capability and the number of SSTS satellites is "an incredible shrinkage of the program. There's much to be modest about," Pike said.

Defense Under Secretary Robert Costello acknowledged to Congress Oct. 6 that the SSTS changes resulted in "decreased performance capabiliity" that would be compensated for ground-based radars and "pop-up probe" rockets launched to take a quick closer look at the incoming warheads and decoys.

Pike charged that the probes and ground-based radars were not designed to do the SSTS satellites' job of discriminating warheads from decoys.

"He's wrong," Schnelzer said of Pike's contention. He said the ground-based radars give a "precise measurement" of motion, not speed, that allows them to distinguish warheads from decoys.

He compared it to distinguishing between a man and a women walking down the street, saying: "It's the body motion that makes he difference. Women walk differently than men.

"The heart of the discrimination is in the ground-based probe and the radar, in conjunction with the SSTS. They work as a team," Schnelzer said.

Pike said that once launched into the vacuum of space, the heavy warheads and decoy balloons travel at the same speed. He contended the main way of distinguishing the decoys from warheads by the amount of heat they emit.

"The idea is that the warheads will be warm and the balloons will be cool. But, I can make the empty balloon look like a warhead by putting a small heater in it," Pike said.