London — West European governments are worried.
Leonid Brezhnev's latest peace salvo, they suspect, will make it still harder for NATO to go ahead with its plans to place new nuclear missiles in West Europe to counter the recent buildup of Soviet SS-20s. And the NATO plan was already in political trouble here.
They see the Soviet President's declaration of a unilateral freeze in deployment of any more of the medium-range SS-20 missiles west of the Ural Mountains as a one-sided propaganda scoop.
A freeze now would institutionalize Moscow's current advantage, they say. Yet , by calling for one, Brezhnev is seen as making his most effective attempt so far to impress European public opinion with the seriousness of Russia's alleged peaceful intentions.
Such fears are being voiced privately at NATO headquarters in Brus o and by individual governments. At the official level, the West European governments have responded robustly and negatively to the Brezhnev announcement -- although some officials concede that Moscow may have moved forward a fraction, though not nearly enough.
British Prime Minister Margaret Thatcher told the House of Commons that Mr. Brezhnev was trying to create a situation in which NATO would concede to Moscow a permanent nuclear advantage in Europe. She made it clear that her government regarded the Soviet offer as a cosmetic gesture with little substance. Britain remains firmly in favor of installing US cruise and Pershing II missiles in Europe if the Russians do not agree to withdraw and dismantle all SS-20 missiles aimed at West European targets.
In Bonn, officials of Chancellor Helmut Schmidt's government took the same strong line. One official said, ''There is little new in what Mr. Brezhnev has to say, but in terms of setting out to mislead the peace people he is saying it more persuasively this time.''
Fears that theSoviet leader may be able to foster stronger opposition to NATO's nuclear plans for Europe underlay such statements. Chancellor Schmidt is under steady pressure from the peace movement, some of it within his own party, to back away from the NATO nuclear missile plan.
West German defense analysts noted that in responding to the Soviet leader's move, NATO governments were in danger of sounding negative and unhelpful -- even though stress was being placed on the widely held belief that the Russians already have 300 SS-20 missiles in place, each with three warheads.
At NATO headquarters, defense planners drew attention to the great mobility of the SS-20 missile. They noted that even from behind the Urals (where the Brezhnev freeze does not apply) the SS-20 missiles could reach targets in Western Europe.
In London a minister of state at the Foreign Office, Douglas Hurd, differed slightly from Mrs. Thatcher in responding to the Brezhnev remarks. He said they represented a step forward in the Soviet attitude, but did not go nearly far enough.
What NATO governments were waiting for, Hurd said, was Soviet readiness to match the Western offer to abandon deployment of all medium-range missiles - the yet-to-be-installed NATO weapons and the already-installed SS-20s.
''It is unreasonable of Mr. Brezhnev to offer a mere freeze in return for us agreeing to leave ourselves in a permanently inferior position,'' he said.
As Brezhnev's comments were given close scrutiny, stress was put in Europea capitals on the fact that they were made on the same day that the current US-USSR Geneva talks on medium-range missiles went into an eight-week recess.
In Paris, officials said there may still be hope that the Russians are in a mood to enter constructive negotiations. In May, when the Geneva talks are due to resume, it is possible that the Russians will come up with new offers, Paris sources said.
Notably absent from most early European assessments of the Brezhnev statement was any emphasis on his implied threat: that if NATO fails to respond to the missile freeze, Russia will take unspecified action against the United States.
American diplomats seemed alarmed by this feature of the Soviet leader's speech. But European politicians and officials appeared more inclined to worry about the impact on the peace movement locally.
Private concern was expressed in London and Bonn that by appearing to reject out of hand the Soviet move, President Reagan might consolidate the European peace movement in its view that he is not serious about achieving a nuclear accommodation with Moscow. Some NATO officials are hoping that Mr. Reagan will come up quickly with a more considered and constructive response.
There are hopes, too, that when the President comes to Europe in June and addresses a NATO summit meeting in Bonn, he will make a major statement on medium-range nuclear weapons calculated to counter any political advantage Brezhnev may reap from his declaration of a missile freeze.