LEONID BREZHNEV has thrust the great strategic issue of the 1980s, the control of "gray area" weapons affecting Europe, into full public view. The weapons are those which the Soviet Union can aim from its own territory at West Europe, and those which NATO can aim from West Europe at the Soviet Union. They are in the "gray area" between the long-range weapons, which the Soviet Union and the United States point at each other and which are subject to control by SALT, and the short-range conventional and tactical nuclear weapons, which are deployed in Europe and have long been under discussion at Vienna.

When the United States enjoyed unquestioned strategic superiority, it didn't matter so much to the European allies what forces Moscow deployed against them. With that superiority gone, however, it matters a great deal, especially since the Kremlin began deploying the mobile, multi-warhead SS20 against European targets. NATO currently has no counterpart to the SS20, and the missile is not subject to control in any negotiating forum. It typifies the developments that have led Europeans to ask, with varying degrees of alarm, whether the United States, having tended to its own needs in SALT, will stay in the game to care for Europe now.

Responding a year or two ago, the United States offered NATO the "neutron bomb." But Jimmy Carter's bobbling and Europe's nuclear ambivalence washed out that initiative. Now the United States is asking NATO to accept Pershing II missiles -- they can reach Soviet targets from West Europe -- and to wrap negotiation of gray-area weapons into SALT III. The Europeans waver between fears of being abandoned altogether by the United States if the Pershings are not deployed and fears of having their fate "decoupled" from that of the United States if they are. But Pershing plans have been advancing and are due to be accepted formally by NATO in December.

It was obviously to head this off that Mr. Brezhnev spoke. He singled out West Germany, at once the keystone of Europe's defense (and the first country slated to take Pershings on its soil) and the ally most committed to detente. You must choose between the Pershings and Ostpolitik, Mr. Brezhnev warned, threatening "extra steps" if Pershings are deployed. As bait, he offered to reduce the number of deployed SS20s -- and to trim Soviet troop and tank forces in East Germany and to take other confidence-building steps.

Leonid Brezhnev cannot seriously think it is fine for the Kremlin to deploy the SS20 but not for NATO to match it. His crude threats, playing on familiar German anxieties, ignore the certain fact that good relations with the East can only be built on confidence in Western defense. Mr. Brezhnev is to be saluted, however, for accepting that SS20s and Pershings are two of a gray-area kind and must be controlled. His other suggestions may help invigorate the long-stalled Vienna talks.

In short, the grand negotiation of the 1980s, in which the American goal must be to strengthen the West's security and unity, has begun.