Experts puzzle over evidence of Soviet strategic defense. SOVIET-STYLE SDI

When satellite photos of construction on a Soviet mountaintop were published in the West late last month, speculation ran rampant. While defense analysts agree that the facility near the Soviet-Afghan border will host military lasers, the agreement breaks down over its purpose.

Some peer at the photos and see an antisatellite or antiballistic missile weapon being deployed. Others look at the same photos and see a research facility, or a laser radar system for tracking spacecraft.

The disagreement over the purpose behind the Soviet facility near Dushanbe reflects not only the fact that the site itself is incomplete. It also reflects the fact that those trying to piece together the size, scope, and threat of Soviet SDI-type research are trying to visualize a completed puzzle with only a few pieces in place.

Up to this point, Soviet negotiators at the arms control talks in Geneva have never formally admitted that their country has a strategic defense program, although they talk about their program ``unofficially'' outside the negotiations.

When it comes to making concrete assessments, says Ashton Carter, a Harvard University physicist and defense analyst, ``The evidence is indirect and tenuous. We're constantly confronting our worst fears, rather than real information.''

According to Robert M. Gates, deputy director of central intelligence, the CIA estimates that the Soviets have spent about $150 billion during the last 10 years on strategic defense.

There are hot disputes about how that figure is derived and contentions it overstates Soviet spending. Even so, says Dr. Carter, there are two important points to be made about Soviet defense efforts. Ground-based weapons stressed

The Soviets place great importance on traditional technologies, such as the antiballistic missile system that protects Moscow. The Soviets have been upgrading the Moscow system, which is the Kremlin's choice for the one deployed system allowed under the 1972 Antiballistic Missile (ABM) Treaty.

The system began with 64 of the 100 permissible launchers and their associated guidance radars. The Galosh interceptor rockets were designed to attack incoming nuclear warheads just before they reenter Earth's atmosphere. The Pentagon says the upgraded system is a two-layer defense, with improved Galosh missiles for attacking warheads just before reentry, along with Gazelle interceptors which will try to destroy warheads that have leaked through the first layer. In addition, the system includes upgraded battle-management radars.

The Moscow ABM system, analysts say, uses technology that is similar to that used at an installation set up to defend the US intercontinental ballistic missile (ICBM) field near Grand Forks, N.D., in the mid-1970s. The US shut down the system shortly after it began operation because it was deemed ineffective.

Soviet spending priorities

James Rubin, assistant director for research at the Arms Control Association, cites estimates that 90 to 95 percent of Soviet spending on strategic defense goes to such ground-based technologies, as well as jet interceptors, radars, and antiaircraft missiles needed to defend against the US strategic bomber force.

The Soviets are developing a new antiaircraft missile, the SA-X-12B, which, along with the SA-10, has the potential for use as an ABM weapon, according to the Pentagon. Some of the radars associated with these systems are said to have been tested during ABM-related activities.

John Pike, with the Federation of American Scientists, points out that there is evidence the SA-X-12B has been tested against tactical ballistic missiles dozens of times, with one successful intercept. Such tests aren't banned under the ABM Treaty, which prohibits tests of antiaircraft systems against strategic missiles.

Debate over new missiles

``Every time the Soviets come out with a new high-performance antiaircraft missile, there's a standard debate within the intelligence community'' over its usefulness against ICBMs, says Mr. Pike. But the missiles are too slow and their radars lack the power and precise imaging needed to incorporate them into an effective ABM system, he adds.

In addition, there remains the issue of the large radar facility at Krasnoyarsk. The US calls it an early-warning radar that, because it lies deep inside the Soviet Union, violates the ABM Treaty's provisions for placement of early-warning radars.

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