Nuclear superpowers in angels' clothing

Like schoolchildren surprised by their teacher in the midst of an eraser fight, the nuclear superpowers are trying hard to look like little angels these days.

The focus of their performance is the Geneva negotiations on nuclear missile forces in Europe. The ''teacher'' is Western Europe - its governments and its peace demonstrators.

The West Europeans do not have a seat at the Geneva table. But they will be crucial to the outcome of the first serious superpower arms talks in more than two years.

In theory, several West European states will begin deploying new American missiles on their soil in late 1983.

The Soviets are intent on preventing this - at the minimum possible cost to themselves. The Americans are intent on making the Soviets pay for a cancellation of the new US missile deployment: specifically, by dismantling their triple-headed SS-20 missiles currently targeted on West Europe.

The more goodwill each superpower can cultivate in Western Europe - it is there that the new US missiles are to be placed - the harder each can push for its negotiating position in Geneva.

That explains the angel act. After months of transoceanic mudslinging, the superpowers have begun talking more sweetly to each other. Each still rejects the other's position on European missiles. Each still accuses the other of cooking up misleading figures on the current missile balance, although the two are coming closer together in their respective numbers. Each says the other poses the real threat to European peace.

But both are being careful to display a convincing seriousness of approach toward the Geneva talks. The very fact of negotiations is demonstratively welcomed in both Moscow and Washington.

''Time will tell'' whether the other side is taking a constructive approach, officials in both capitals say. But if the other side is serious, well then, we're more than ready to reciprocate. We are ready, too, to listen to ''other ideas'' than those we've put forward.

In keeping with the holiday spirit, both US and Soviet negotiators in Geneva have even agreed to forswear self-serving leaks to the news media. Both sides, at least for now, seem to be holding to the agreement.

''Time will tell,'' as the current saying goes, just how long the blackout on details of the Geneva talks will last. The missile negotiations promise to be lengthy and to be complicated further by the start of strategic arms talks next year.

Even assuming both the US and the Soviets are genuinely serious about the ''Euromissile'' talks - diplomats here see no reason so far to doubt this - the superpowers' negotiating positions remain distant.

As the conference drags on, with Western Europe watching, each side may well be tempted to offer its own version of what is going on behind closed doors; to suggest, in effect, ''We are being serious, just as we told you. But the other side. . . .''