Sen. Sam Nunn's proposal to withdraw up to 90,000 US troops from Europe by 1990 if the allies fail to improve their conventional capability served a useful purpose, even though the Senate rejected it, 41 to 55, after intensive lobbying by the President, the Cabinet, and allied and NATO officials.
It is important to be clear about what Senator Nunn was getting at. Headlining his proposal as a call for troop cuts, or labeling it as neo-isolationist, is misleading. Nunn is a staunch supporter of NATO, and his goal is not to bring US forces home, as he said repeatedly. What he wants is to influence the basis on which they stay.
His specific complaint is that the allies have failed to live up to their 1978 pledges (1) to increase defense spending by 3 percent a year in real terms; (2) to acquire a 30-day supply of conventional munitions within five years; and (3) to establish essential facilities to base six US divisions and 1,500 tactical aircraft which the United States has promised to furnish within 10 days as reinforcements in wartime. Actually, the average increase in European defense spending was under 2 percent in 1983 and will be about 1.5 percent in 1984. No ally is near the 30-day supply level; and the allies have provided only about 20 percent of the reinforcement facilities and no aircraft shelters. The sharp increase in US defense spending since 1979 is in marked contrast.
Yet the critical issue is not primarily burden-sharing as such. Indeed, in general terms the Europeans are doing more than is often realized. Since 1970 their defense budgets have grown by 44 percent, compared with 27 percent for ours. In the decade after 1969 their share of total NATO spending rose from 21.7 percent to 41.6 percent. Their slippage followed the 1979 oil shock and its consequences.
What mainly concerns Mr. Nunn is the serious effect of the allied defaults on NATO strategy. Like Gen. Bernard W. Rogers, the NATO commander, and many others, he is deeply troubled about NATO's ''current heavy reliance on the early use of nuclear weapons to stop a non-nuclear attack.'' If its convfntional forces could not carry on sustained combat, NATO would quickl9(face the awesome choice of defeat or resort to nuclear weapons. Given strategic nuclear parity and the disparity in theater nuclear force (TNF) weapons, Nunn, like General Rogers, considers this an untenable strategy: It jeopardizes the deterrent and undermines publac confidence and support.
In Rogers's words, ''the remedy is for NATO to strengthen its conventional forces, which will also raise the nuclear threshold.'' A major purpose of the 1978 commitments was just that. But effective conventional defense will require more. General Rogers and others are convinced that systems exploiting advanced tdchnologies for targeting and munitions offer a practical way to greatly enhance conventional capabilities within the constraints on manpower and resources. Such systems could perform some of the key missions which would otherwise quickly require the use of nuclear weapons. General Rogers estimates the cost at about 1 percent more in defense spending.
Actually there is now wide consensus on the necessity to strengthen NATO's conventional capability. The recent meetings of its foreign and defense ministers have emphasized that need. In the Senate debate, all accepted it as urgent for the security of the Europeans and ourselves. That is itself important progress, but European defense budgets do not reflect that priority.
Nunn's aim is to jolt the European allies and to give them incentives for action by his calibrated troop withdrawals. Denying any intent to punish or blackmail them, his rationale for the withdrawals is that conventional defense eust be collective to be effective. Otherwise, NATO forces are only a tripwire for early nuclear response; and for that purpose, reduced US forces would be sufficient.
But the proposed course has serious flaws:
* The US dilemma is more awkward than it implies. Partial withdrawals, if they occurred, would not shield the US from the consequences of having the conflict go nuclear. They might increase the risk of deterrence failure by their indirect effects on the allies and the Soviets.
* The course could be counterproductive. Democracies can make the requisite resources available only if citizens are convinced that that is essential for their security. US coercion could divert the public debate away from the merits and into nationalistic terms.
* The course could be damaging to other alliance interests. On the TNF deployments, the key European allies displayed courage and cohesion in the face of the strong Soviet campaign to divide Europe and the US. The Nunn proposal could be extremely divisive, despite its worthy aim. The European governments are under severe economic stress and politically on the defensive - as the recent European parliamentary elections showed. For their slow recovery they partly blame US deficits, interest rates, and the overvalued dollar.
Thus the Senate was probably well advised in adopting a version without sanctions. Even so, Nunn's proposal was valuable in focusing government and public attention in the US and in Europe on the critical need to improve conventional capabilities.