'Star-wars' defenses: too costly, can be overwhelmed, study says

A group of distinguished scientists and nuclear strategists warns that trying to defend the United States against ballistic missiles would cost hundreds of billions of dollars and be extremely vulnerable to overwhelming attack.

In a report released yesterday by the Union of Concerned Scientists (UCS), these experts examine in detail each segment of a proposed multi-layered defense against attacking missile warheads and the advanced technologies involved. In essence, they say, it won't work.

Their conclusion is even more sobering: It would ''radically transform the context of US-Soviet nuclear relations, setting in motion a chain of events and reactions that would leave both superpowers much less secure. Deterrence would be weakened and crisis instability increased. Damage-limitation would be undermined by a greater emphasis on the targeting of cities. . . .''

Among those contributing to the report are: Hans Bethe, Nobel Laureate in physics who worked on the Manhattan project; Peter Clausen, a former Department of Energy and CIA analyst; Richard Garwin, a nuclear strategist and Pentagon adviser; retired Adm. Noel Gayler, former director of the National Security Agency; and physicists Kurt Gottfried of Cornell University and Henry Kendall of MIT.

In a dramatic speech a year ago this week, President Reagan called for research into a system that would render attacking nuclear missiles ''impotent and obsolete.'' The Pentagon wants to spend some $2 billion next year on such research, a sum that Reagan administration planners say will increase to $24 billion through 1989. Officials see this as a hedge against Soviet advances in ballistic-missile defenses, as well as a counter to Soviet strategic weapons which capitalizes on a US lead in most of the sophisticated technologies involved.

Intercontinental ballistic nuclear weapons would take about 30 minutes to travel between the Soviet Union and the United States. Experts divide this flight path, and the areas in which defenses might be deployed, into three tiers: the boost phase, or first several minutes when the rocket engine is firing; the midcourse phase, in which the warheads, decoys, and other devices have separated from the missile and are flying ballistically in an arc outside Earth's atmosphere; and the terminal phase, when the nuclear warheads are streaking back down through the atmosphere toward their targets.

The Soviet Union now has about 1,400 ICBMs. Once launched, they could release tens of thousands (perhaps hundreds of thousands) of warheads and decoys, thus presenting an extremely difficult challenge to a defender, who would have to assume for most of their flight time that each was a nuclear weapon. Therefore, most experts say any successful defense would have to concentrate on the boost phase, when the missiles' rocket plumes are easily detectable and during which there are relatively fewer targets to defend against .

Some analysts say this would not be too difficult. In a new book, former Defense Intelligence Agency director Daniel Graham (a retired Army lieutenant general) claims that ''within five years, at a cost of $12 billion, the United States could deploy a two-layered fleet of satellites (firing interceptor rockets) that would filter out 98 percent of a Soviet missile launch.''

But this is a distinctly minority view not shared even by those who support the President's program.

The UCS experts examine the laser, directed energy, and kinetic energy defenses being studied by the Pentagon and conclude that none could work sufficiently to prevent many warheads from reaching US targets. Each is vulnerable to attack or ''spoofing,'' they say, and it would be easier and cheaper for the USSR to expand its strategic forces than it would be for the US to counter them. ''I would far rather be on the side of penetrating this ballistic missile defense than on the side of building one that works,'' Dr. Garwin told reporters yesterday. He and the others recommend a research effort more modest than planned by the Reagan administration.

The authors warn that deploying (or even testing in space) a missile defense system would violate the Anti-Ballistic Missile Treaty of 1972 and that broader nuclear arms control efforts would collapse. They urge ''equitable and verifiable deep cuts in strategic offensive forces and immediate negotiations to ban all space weapons.''