It is painful but politically necessary for Americans to recognize that today, despite Moscow's expansionist record -- up to and including Afghanistan -- an increasing number of Western Europeans regard President Reagan as a bigger threat to world peace than President Brezhnev.

The president's blunt and homely style, which has endeared him to so many Americans, is being seized on by his enemies in Europe to give substance to the preposterous caricature of a "might is right," trigger-happy cowboy. When Reagan muses aloud that "the only defense is, well you shoot yours and we'll shoot ours," he is only restating the NATO policy of nuclear deterrence. Yet the words can be made to sound as if he accepted violence and endorsed Gen.Robert Schweitzer's view about "the drift towards war."

Nervous Europeans are hardly comforted by the news that the apocalypse-minded general has been transferred from the White House to the Pentagon and so reincorporated into the military apparatus. In effect, the president and the general seem to disagree only on a matter of timing. For the president, the "drift towards war" has been reversed by his own $180 billion proposal for upgrading the deterrent. The drift was real "when we were unilaterally disarming (a concept which astounds Europeans) and had a widening window of vulnerability...."

To the untutored European ear, the very phrase "window of vulnerability," which keeps cropping up in Washington, suggests that in a nuclear war, the Americans, unlike the rest of the world, hope to buy invulnerability. The president's now-famous remark on the possibility of a war in Europe in which "neither of the major powers pushed the button," seemed to confirm the epithet of the British pro-Soviet trade union leader, Alex Kitson, which earned him a roar of applause at the recent Labour Party conference: "A limited nuclear war means a nuclear war limited to Europe."

To the Pentagon, "the window of vulnerability" has a precise and technical meaning: It symbolizes the new threat posed by the current Soviet monopoly of long-range land- based missiles accurate enough to destroy the silos encasing the missiles on the other side of the world. Many U.S. officials concede that the threat is nonexistent, yet defend the program as a useful "signal" to Moscow indicating that the Americans cannot accept inferiority in any sector of nuclear arms.

After Vietnam, after Iran and now after the murder of President Sadat, it is easy to see why Americans feel they have been kicked around too long and respond eagerly to President Reagan's reassertion of U.S. power (even though none of these setbacks would have been averted by more nuclear weapons.)

What Washington is only now beginning to appreciate is that these signals go not only to Moscow but also to Western Europe. And last week the Kremlin was remarkably quick to exploit the growing European fear that the Americans have indeed now accepted the inevitability of conflict and are actively preparing for war.

Most Kremlin-watchers would accept the testimony of Galina Orionova, the young defector from Moscow's official Institute on the U.S.A. and Canada, who has identified the breakup of the Atlantic alliance as the prime aim of Soviet diplomacy. In that case, the Russians should be reserving a Lenin Prize for the advisers who encourage the president to brandish the big nuclear stick while leaving Brezhnev a virtual monopoly on the peace movement.

The president himself has protested against Soviet propaganda designed to drive a wedge between the United States and some of its closest allies, yet he seems unaware of how much he and his associates have contributed to the growth of the left-wing unilateralism and pacifism which he deplores.

In Britain, these views have captured the Labor Party, while its previously dominant pro-NATO leaders have quit to form their own political party. Unless these succeed in breaking Britain's traditional two-party mold, the next prime minister will probably be Michael Foot, a dedicated unilateralist who has always felt closer to "socialist" Moscow than to "capitalist" Washington.

In West Germany the peace movement has recently demonstrated its power by amassing in Bonn an unprecedented quarter of a million antinuclear protestors and it is uncertain whether, without the now ailing Chancellor Helmut Schmidt, the ruling Social Democratic Party will remain loyal to NATO.

In France, although President Mitterrand personally is tougher than his predecessor in his dealings with Moscow, he has brought into his government several members of the unconditionally pro-Soviet French Communist Party.

Nor is neutralism confined to the pro- Soviet and pacifist left. Mainstream sentiment has clung to the Nixon-Kissinger notions of detente: the existence of interlinking interests between the two superpowers. Indeed, they have taken the concept further, suggesting that it is now the task of Western Europe to mediate between the two giants. This was the theme of a recent article in The Times of London entitled "Two Underdressed Emperors," which cast the young leftwing demonstrators in the rule of the mythical child, observing that both emperors have no clothes on.

The common values cementing the Western alliance were reaffirmed in President Carter's dedication to human rights. President Reagan's repudiation of any moral restraints in the power game has contributed to the European feeling that the two superpowers are merely defending their conflicting national and imperial interests. Indeed, one French minister, Pierre Cot, recently argued that the United States in Latin America was more objectionably interventionist than the Soviet Union in Africa.

If the present administration does not want to preside over the disintegration of NATO, it may have to show more sympathy for the European pressure to start immediately -- and continue incessantly -- trying, with or without success, to negotiate arms restraint and disarmament. This is not only because of a preoccupation with holding off the unilateralist challenge. It is also based on the almost unanimous view in Western Europe that the Russians, however inimical to western civilization, are not suicidal and that nuclear war would be as calamitous for them as for the rest of Europe.

Is it sensible in these circumstances for the Americans to continue to put on as much pressure as they did at the conference of defense ministers in Gleneagles, Scotland, last week, to induce the Europeans to accelerate the installation of cruise missiles and Pershing IIs on European soil? Few strategists would argue that these weapons are militarily indispensable to NATO defense, but the U.S. administration has come to regard their emplacement as a litmus test of loyalty to the western alliance.

We need to acknowledge that, partly because of the Reagan rhetoric, the European mood is very different today from what it was three years ago, when Chancellor Helmut Schmidt himself demanded these weapons to offset still-continuing installation of Soviet SS20s targeted on all NATO installations in Europe.

In the present climate, we can expect passionately committed pacifists and leftists to use violent physical resistance against the installation of U.S. mobile weapons. In their present crusading mood, the youthful campaigners would be ready to risk their lives and -- if the Communists have any luck -- to lose them in civil battles which would make the old Vietnam demonstrations look like kindergarten games.

Cruise missiles may be necessary to prevent the Soviet leaders using their nuclear preponderance in Europe to threaten and to intimidate. But we now know from the Pentagon itself that the cruise missiles can be installed in submarines. The White House has asserted that this "does not diminish the critical need to deploy ground-launched missiles and Pershing II ballistic missiles to counter the massive Soviet buildup of theater nuclear forces in Europe."

Perhaps NATO should reexamine this "critical need" in political as well as military terms. If the dispute over the land missiles could be averted, there would still be anti- American agitation, fanned from Moscow, but it would enjoy declining support. For the vast majority of West Europeans, the U.S. administration would recover the status enjoyed by all its predecessors since Truman: senior partner in the business of preserving peace.