Brussels — Buoyed by past successes, the West's peace movement took to the streets again over the four-day Easter weekend saying it had only begun to fight . . . but prompting others to wonder whether it had made war more, rather than less, likely.
Hundreds of thousands of demonstrators turned out to protest in inclement weather across Western Europe only days after President Reagan announced that the US was effectively abandoning its so-called ''zero-option'' negotiating position at the Geneva nuclear arms reduction talks.
Soviet Foreign Minister Andrei Gromyko immediately rejected the new US ''interim proposal,'' leading some analysts here to reiterate the oft-stated line that the peace movement is playing into the hands of the Soviet Union.
Whatever the peace movement has done, it has divided public opinion in Western Europe to a far greater extent than any other issue since World War II.
Few observers here doubt that the strength of the movement reflects a genuine concern among a large segment of the population in Western Europe. Opinion polls in Britain show that more than half of those questioned oppose the deployment of cruise missiles in Western Europe. Polls in other countries have recorded similar readings.
But just as strikingly, the anti-deployment Social Democrats in West Germany lost to the pro-deployment Christian Democrats in the March elections, reflecting a strong pro-NATO feeling in the population. Moreover, the antinuclear movement is weakest in the two West European countries where the Communist Party is strongest - France and Italy.
The question being asked by strategists in the West is how effective the growing peace movement can be expected to become - and whether it will force further changes in the NATO and Soviet negotiating positions.
Some Western analysts have gone so far as to argue that the movement, in fact , had no influence whatsoever on President Reagan's decision to ''climb down'' (at least temporarily) from the zero option. They say that most West European governments simply came to the inevitable conclusion that the plan was ''unattainable.''
To have asked the Soviets to dismantle their entire nuclear arsenal, they said, in exchange for a promise by NATO to drop plans to deploy 572 new nuclear missiles in Western Europe, beginning later this year, was unrealistic. But not to have tested the idea on the Soviets at all would have been just as unrealistic, those same analysts insist.
Where the Western European peace movement may have had its greatest ''success'' is in the Soviet Union.
''Even this Easter weekend,'' the Economist magazine said in an editorial, ''the ban-the-bomb campaign is already exacting its toll of Western weakness. It may have pushed President Reagan into making a premature new offer about nuclear weapons in Europe which would have been better saved until later in the year.''
And it may be encouraging Soviet leader Yuri Andropov, the magazine said before the Gromyko news conference April 2, ''to reject even this offer in the hope that Western Europe demonstrators will then help him force Mr. Reagan into a further climb-down.''
Spokesmen for the peace movement have welcomed Reagan's interim proposal as a sign that the two superpowers have begun to negotiate seriously. But they have also said they will redouble their efforts in this make-it-or-break-it year for the movement.
What could happen, some argue, is that the peace movement may have an even greater ''success'' when the Geneva talks reconvene and that this time the success will again be with the Soviet negotiators. Encouraged by the peace campaign, the scenario goes, they will reject any serious offer the US negotiators put on the table because they will believe they can get something even better. No agreement will be reached. The talks will break off.
That this will ever happen is discounted by many - not the least of which are many persons active in the peace movement.
Recent reports from Moscow have suggested a certain flexibility in Soviet thinking despite the persistent restating of the official line, namely, that even a partial deployment of NATO nuclear missiles in Western Europe would present a ''new threat'' to Moscow.
Those reports have hinted that the current Soviet position could be altered to take account of the new US offer when the superpower negotiators reconvene.
[But the official Soviet media accused Washington Monday of wanting the Geneva arms talks to fail so the US could deploy nuclear missiles in Europe, United Press International reports.]