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.

The Soviets claim it is designed to track objects in space. In September, Rep. Thomas J. Downey (D) of New York and other US lawmakers and scientists were allowed to tour and photograph the site. Though confirming that the site is still far from complete, the information stemming from the visit has tended to confirm the US view that the radar is designed to help warn of a nuclear attack.

Soviet space-based research limited

The second of Dr. Carter's two points is that ``as near as we can see, there is not nearly as much visible activity'' in the Soviet Union on space-based weapons research. Yet US defense officials apparently think they have seen enough to describe at least the broad outlines of a Soviet program exploring the same kinds of exotic technologies as the US Strategic Defense Initiative.

According to the Pentagon, the Soviets are developing laser and particle-beam weapons. They are also said to be working on so-called kinetic-energy weapons, whose small, high-speed projectiles destroy a target by colliding with it. The Pentagon says the Soviets could deploy prototypes of antisatellite or antiballistic missile weapons based on these technologies by the mid- to late 1990s.

Laser development compared

The Soviets began research into laser and particle-beam weapons in the 1960s. By contrast, the United States has been exploring the concept of using particle-beam weapons for ballistic missile defense since the 1950s, according to Alexander Flax, former US Air Force chief scientist and assistant secretary for research and development.

The current Soviet directed-energy effort would cost the US about $1 billion a year to duplicate, the Defense Department says, adding that some 10,000 Soviet scientists are involved in the work. Current spending for US directed-energy weapons stands at about $850 million.

Soviet `advantages' seen

One of the major differences between the US and Soviet program in developing such exotic weapons has been the Soviets' consistency.

Simon Kassel, a specialist on Soviet technology at the RAND Corporation, points out that the Soviets have pursued their research ``at a much higher level than ours'' over a longer period of time. He says that ``now or in the near term, the Soviets could have a proof-of-principle test'' for some of their directed-energy weapons technologies.

Of most immediate concern to the US military is the potential for the Soviets using directed-energy weapons - even ground-based - against US satellites. The Soviet Union has already deployed the world's only operational antisatellite weapon using more conventional rocket technology. Late last month, Gen. John L. Piotrowski, head of the US Space Command, said that Soviet lasers at the Sari-Shagan test site could disable satellites in low-Earth orbit and damage those at higher altitudes.

US holds technology lead

In assessing individual categories of technology needed to develop space-based ballistic missile defenses, many analysts give the Soviets an edge in high-energy lasers and power generation. But they also give the US the edge in sensors, computers, and computer software, which are crucial to knitting individual weapons into a system.

Moreover, a range of countermeasures are available to designers of both sides that would help blunt the effects of antimissile or antisatellite weapons.

Judging battle strength

One congressional national-security specialist suggests that when looking at the potential for fighting battles in or from space, there are four factors to look at, weapons technology being only one.

The others include war-fighting doctrine, the infrastructure to support space operations, and the military institutions charged with carrying out the doctrine.

For the United States, he says, mastering the technology would be only the first step. The Soviets, he continues, have a long-established military branch charged with air and space defense. They have a well-defined doctrine. And they have an ability to launch heavy payloads which not only exceeds that of the US, but also is twice what the US estimates the Soviets will need for the military and civilian roles Western intelligence officials can foresee.

For the Soviets, he concludes, solving the weapons technology problem would appear to be the last step toward gaining an edge in the military use of space.

Second of three articles. Tomorrow: The ABCs of US-Soviet arms reduction.