In the 30 years since the Soviet Union developed its own nuclear weapons, a recurring nightmare has beset U.S. military and intelligence circles: That the Russians might achieve a solid defense against incoming American missiles, tempting them to try a "first strike" nuclear attack on the United States without fear of devastating retaliation.

The Kremlin has the same fears about us, even though American presidents since the dawn of the nuclear age have asserted that the United States would never strike first.

The Anti-Ballistic Missile Treaty of 1972 was intended to calm fears on both sides. But concern is mounting in the intelligence community that the Soviets have been developing an ABM capability anyway -- in possible violation of the 1972 treaty. The Soviet-U.S. agreement, incidentally, is due for review a year from now, and its extension is expected to touch off intense debate.

The areas of Soviet research on anti-missile defense are outlined in a series of 14 top-secret intelligance documents shown to my associate Dale Van Atta. One was a 1979 memorandum from then-defense secretary Harold Brown to President Carter, which warned that "Soviet ABM R&D activities have led to concern over the development of a quick breakout capability" -- that is, the ability to launch an attack with impunity.

Here are some of the concerns expressed in the intelligence documents:

The Russians may already have perfected a semi-mobile ABM system capable of being deployed rapidly.

The Soviets have also tested surface-to-air missiles (SAMs) as weapons against incoming missiles. More than 100 Russian cities have SA5 interceptor missiles in position with the radar systems that will guide them to their targets. The Soviets have already tested upgraded SA5s for use against faster, higher-flying missiles. At least five such tests were conducted in the early 1970s, with the missiles reaching altitudes in excess of 125,000 feet. There is one optimistic note in the report on these tests: In each case "the missiles appeared to have malfunctioned, and the higher altitudes achieved resulted from uncontrolled flight."

The Soviets have four large "phased-array" radars under construction. Linked to so-called "battle management" radars, these would provide good anti-missile capability.

"These new radars will provide better target-handling and tracking data and more accurate impact prediction," a Pentagon intelligence report states. "They are also assessed to be capable of providing accurate data for direct ABM support."

A modification of the ABM treaty provided that each side could have only one anti-missile system near a particular city, with no more than 100 missile launchers per city. The Russians have been building their ABM system around Moscow and have deployed as many as 64 launchers.

The treaty did nothing to slow down the Russians. As one top-secret CIA report noted, "The number of [test] flights apparently related to ABM activities has remained unaffected by the treaty."

Meanwhile, the United States shut down its own "Safeguard" ABM program at Grand Forks, N.D., in 1976, when Congress cut off funds for it. Since then, however, the Pentagon has been continuing active research on ABMs at the rate of about $250 million a year. The possibility of reviving an ABM system, particularly as a means of protecting the admittedly vulnerable MX missile system, has been gaining increased support at the Pentagon.

If U.S. anti-missile defenses are not resuscitated, the generals will keep having nightmares about a Soviet first strike.