Reagan's long-awaited signal on arms control

In his latest move on the chessboard of arms control, Ronald Reagan seeks to reduce dramatically the total strategic nuclear forces of the US and the USSR. If there is one word to describe his goal, it is stability.

There are two reasons behind Mr. Reagan's proposal, which he disclosed May 9 in a commencement address to Eureka College, in Eureka, Ill.

First, the United States wants to halt the upward spiral of nuclear weapons production and deployment that has given both sides what many experts feel is overkill capacity. Second, the US administration aims to close what it calls the ''window of vulnerability'' by enticing the Soviet Union to give up some of its most threatening weaponry.

Here, President Reagan is calling on the Soviets to reduce their advantage in accurate land-based intercontinental ballistic missiles (ICBMs), which seriously threaten similiar US weapons and increase the possibility of a successful first strike or nuclear blackmail.

In exchange, the US would give up its edge in total nuclear warheads and bombs (approximately 9,000 to 7,000). But if the Soviets refuse the carrot, Reagan's stick is to proceed with the United States' own very accurate, well-protected missiles (particularly those launched from submarines) and let the arms race continue. It is felt here that the US could more easily afford such continued escalation.

Reagan proposes that each side reduce its total arsenal of strategic missile warheads by one-third, to about 5,000, with no more than half of these contained in land-based missiles. The US currently has 1,050 ICBMs and 650 SLBMs (submarine-launched missiles) with some 7,200 missile warheads. The Soviet Union has 1,400 ICBMs and 950 SLBMs with some 6,300 warheads.

To meet these goals (over a five- to 10-year period), the Soviet Union would have to cut more missiles than the US. But the United States would have to reduce its strategic nuclear arsenal by a greater number of warheads.

''The effect of the reductions are both to reduce and if possible eliminate the destabilizing systems,'' said a senior administration official. ''And we believe that the most destabilizing systems are those large, heavy Soviet ICBMs that they have unilaterally built up over the last 10 to 15 years. They're the most threatening systems to the overall stability of the strategic balance.''

But ''there is something in this for both sides,'' this official continued. Here, he was referring to the new US Trident submarine system, particularly the D-5 missile with multiple warheads that will be as accurate as Soviet land-based ICBMs but nearly invulnerable to first-strike attack.

Perhaps as important as the number and type of launchers and warheads will be the US proposal to limit ballistic missile throw-weight to less than the current American level. This is a measure of how much payload a missile can carry. The US total throw-weight now is about 4 million pounds, compared to nearly three times this much for the Soviet Union.

Throw-weight is likely to be one of the most seriously contested points during negotiations between the two countries, as is the issue of which aircraft are to be counted as strategic weapon bombers. As in the past, the US wants to include the Soviet Backfire bomber, an aircraft the Soviet Union insists is capable for shorter ranges only.

''We shall insist on verification procedures to insure compliance with the agreement,'' the President said May 9.

Now, only ''national technical means'' -- chiefly satellites -- are employed to verify treaty compliance. Particularly as mobile missiles are deployed, it is felt that better on-the-ground verification will be necessary.

The administration and its critics agree the US has a better mix of strategic forces while the Soviet Union concentrates on the land-based leg of its triad. The administration feels both sides could deliver devastating blows, even after a first strike. But the Soviet Union, it is felt here, has strong momentum in developing and deploying heavy, accurate missiles aimed at US strategic forces.

The goal, says a senior arms control official, is to reduce this instability while maintaining enough ''residual military power to contribute to deterrence.''