Aging missiles: a useful sideshow to superpower arms talks. As the superpowers jockey for an arms deal, a key bone of contention is the presence of Pershing 1A missiles in West Germany. Disruptive though this tussle could be, it is a fight with benefits for the US, Soviets, and West Germans.

The 72 aging Pershing 1A missiles may be only a sideshow when compared with the 1,700 modern medium-range nuclear missiles that would be destroyed under the superpower arms-control agreement that currently is shaping up. But they promise to be a particularly useful sideshow for Moscow, Washington, and - when viewed in hindsight - probably even for Bonn.

First the Soviets. They have run a forceful campaign against the 720-kilometer-range (450-mile) West German Pershing 1As. The Soviets call the Pershing 1As the major remaining barrier to an agreement on worldwide elimination of all superpower intermediate-range missiles (INF), with ranges between 500 km (310 miles) and 5,500 km (3,440 miles). Moscow says since the warheads are American, these weapons should be included in the superpower ban. The US rejects this, arguing that the missiles themselves belong to a third country for whom it cannot negotiate.

Various Soviet spokesmen, including Foreign Minister Eduard Shevardnadze, have stressed there will be no INF agreement without a resolution of the Pershing 1A issue. But the Soviets haven't totally ruled out what Westen diplomats believe is the most likely solution: letting the missiles expire of obsolescence by the early 1990s - within the same time frame in which an INF agreement would be implemented.

Until the scheduled September meetig between Mr. Shevardnadze and US Secretary of State George Shultz in Washington, the Pershing 1A issue is a useful brake for the Soviets on the otherwise far advanced INF negotiation. The brake comes at a point when Moscow would like to let the trategic arms control talks (which have been taking place in Geneva at the same time) catch up with the INF talks to press for an American decision on the Strategic Defense Initiative program and comprehensive arms control.

Clearly, Moscow's original intention last February in ``delinking'' INF from arms control in strategic offensive and defensive weapons was, paradoxically, to get some momentum going in the easiest negotiation - INF - in hopes of transferring that momentum to strategic offensive and especially defensive negotiations. Aligning the INF and offensive strategic arms reduction (START) talks to mature together at the time of any superpower summit in the fall could help do this.

For the Americans, allowing their arms to be twisted into letting the Pershing 1As become obsolete resembles Br'er Rabbit being thrown into the brier patch. Since the West Germans have refused to take on the domestic political fight of modernizing the systems, the West would only be giving away as a negotiating concession an option that it never could implement anyway.

So long as the Soviets continue to demand that the Pershing 1As be included in the formal superpower INF agreement, the US can an will win points with Bonn by refusing to do so. Nuclear ``deterrence,'' is both psychological and military, and requires reassuring one's allies as much as dissuading the adversary. Thus, such a Soviet invitation to US defense of Bonn's interess is a welcome opportunity to repair disarray in Bonn-Washington relations.

These relations were strained following the superpower summit in Iceland last October and the INF negotiations last spring. The front-line West Germans were upset by theUS's willingness, without consulting its NATO allies, to negotiate away all nuclear missiles in Iceland, and by the subsequent American, British, and French readiness to negotiate away all INF missiles only down to the 500-km range. Missiles, less than 500-km range, primarily would devastate German territory.

For the West Germans, then, the 720-km Pershing 1As, militarily useless though they might be in the absence of other INF weapons, become an important symbol that NATO's long-standing threat of nuclear escalation in case of Soviet conventional attack still would go beyond German soil to cover Poland and the westernmost tip of the Soviet Union.

And the fact that Bonn protested at the course of the INF negotiations and won American assurances of preserving the Pershing 1A, probably has bolstered West German confidence in the ultimate outcome of superpower arms control. This especially should be so if INF arms control turns out to be twinned with massive superpower reductions in strategic arsenals that would usher in an improved East-West climate.

But there are potential alliance frictions. The French, always nervous about any possible West German acquisition of the nuclear weapons Bonn has renounced, hardly like the West's current classification of the West German missiles with their American warheads as ``third country systems'' that do not belong to the US. And the French, British, and Americans - who all want to avoid negotiating numbers of tactical nuclear weapons with the Soviets - are unhappy about the recent West German suggestion of a trade-off between the Pershing 1A and Soviet Scud missiles in Eastern Europe in the less than 500-km range.

There also are potential pitfalls for the Soviets. Shevardnadze hoped in part to play on French sensitivity about West German acquisition of nuclear arms by demanding to know this month whether Bonn was violating the Nuclear Nonproliferation Treaty with the Pershing 1As.

The tactic backfired, not only because this gave the US another chance verbally to defend West Germany against Soviet ``intimidation,'' but also because the bulk of Western reporting, to Shevardnadze's regret, was deflected from the package of Soviet peace offers that Moscow wants to highlight.

Moreover, if Moscow eventually is going to settle for letting the Pershing 1A wither away, then it must not play the issue too hard now, for fear of losing face in any future settlement.