HAD YOU forgotten that the Americans and Soviets have been over there in Geneva negotiating quietly on nuclear forces in Europe? Leonid Brezhnev forcefully reminded everyone yesterday by making one of those loud, bold interventions that the Kremlin is given to making when things get difficult at the table. It came pretty much on schedule, like the second stage of a rocket, just as the Geneva talks went into recess. It was a statement simple and dramatic in form, designed to appeal over the heads of the negotiators to an anxious and somewhat confused Western public.

The Soviet Union will unilaterally freeze its missile force west of the Urals aimed at Europe, Mr. Brezhnev declared, if NATO does not deploy new Pershing II and cruise missiles, or until agreement on mutual reductions is achieved. Moreover, he said, later this year his government will unilaterally remove "a certain number" of missiles, barring "a new aggravation of the international situation." That was the carrot. The stick: if the United States deploys the new missiles, creating "a real additional threat to our country and its allies," Moscow would "put the other side, including the United States itself and its own territory, in an analogous position. This should not be forgotten." He went on to nag President Reagan to start START, the full-scale strategic-arms talks meant to succeed SALT, and made the usual gallery play.

To one part of this statement, President Reagan yesterday had a prompt response. The Soviet freeze, he said, is not good enough. He's right. In November when the talks began, Moscow held what a unanimous NATO regarded as a dangerous imbalance--250 to 0--in the most menacing variety of European missiles, mobile triple-headed SS20s. In the four months since, Moscow has increased this margin to 300 to 0. The freeze that Mr. Brezhnev offers with an air of self-denial masks an unprovoked expansion of a formidable force of weapons meant to intimidate.

But, insist the Soviets, other European-nuclear categories, such as the bombs carried by NATO planes and the independent deterrents of Britain and France, must also be counted. Must they? That is precisely what the Geneva talks are about. The United States argues that the Soviet SS20s are in a class by themselves and must be reduced to zero, or countered. The Soviets contend that other Western weapons, regardless of their different physical and political characteristics, threaten them, too.

From the start, the Reagan strategy has been to show that NATO is firm and united on the matter of the special menace of the SS20s. Mr. Brezhnev brought the Soviet strategy into full view yesterday. His position is properly outrageous; it is a negotiating position.