IT COULD YET happen that the Soviet Union will succeed in scaring the Europeans into denying or deferring indefinitely a decision to deploy new missiles to match the currently unmatched Soviet SS20s, whose number grows with each passing week. The prospect of such a result, signifying a major split in the Atlantic alliance, may appear so sweet to the Kremlin as to be considered well worth the risk of defeat.

It should be understood, however, that if Soviet policy is defeated--if the promised start is made on deploying the new American missiles, especially the quick-attack Pershing IIs that the Soviets profess most to dread--that will be a result Moscow has brought on itself. For it has been open to the Soviets from the start of the INF talks 16 months ago, as it still is, to head off the possibility. They can accept President Reagan's offer of zero-zero: no Euromissiles for either Soviets or Americans. This would restore the status, long mutually accepted as balanced and tolerable, that Moscow upended with its SS20s.

Mr. Reagan's first negotiating position, anticipating a full deployment of 572 new missiles unless Moscow scaled back to zero, was principled. It was also too much for European nerves and politics to bear. Essentially--and necessarily--to accommodate Europe, the president yesterday fell back to a position under which Moscow and Washington would agree to an equal number of Euromissiles: the more Moscow dismantles, the fewer Washington will put in. So into their calculation of risks and benefits the Russians must now crank the probability that the new Reagan position improves the chances of some American deployment.

The Kremlin had already conceded the illegitimacy and lack of strategic necessity of its current (and building) level of 351 SS20 missiles by offering to reduce it to the number (162) of French and British launchers, if there were no American deployments. Notwithstanding its negotiator's hint to the contrary in the famous "walk in the woods" in Geneva last summer, the Kremlin continues to insist on factoring in those European launchers.

How can this be done? One possibility is for the two superpowers at some point to merge their Euromissile talks into their strategic weapons talks or some larger context. This is a way to deal with the British and French missiles, which do pose a certain threat to Moscow, and also with the fact that American Euromissiles, though intermediate in range, are strategic in that one superpower would train them on vital targets of the other.

What Mr. Reagan said yesterday seemed to us entirely consistent with such an eventual merger. The West would be at a serious disadvantage in heading that way, however, if Europe caved on deployment first.