A grass roots movement against nuclear armaments is growing in several key Western European countries, leading some Western officials to worry that it could become a political force strong enough to erode NATO unity.

The anitnuclear activists plan rallies and conferences this spring to dramatize their cause, timed to coincide with a round of political and military strategy sessions by Western alliance officials.

The demonstrators' specific objective is to prevent deployment of new U.S.-made nucler missiles in Europe, now planned to begin at the end of 1983. But their agitation also reflects broader concern about the dangers of the nuclear standoff on their continent.

When the decision to deploy the missiles was made in December 1979 -- coupled with an offer to negotiate with the Soviet Union to limit such weapons -- it was hailed as a momentous political achievement. Officials said then it was meant to signal the solidarity of the North Atlantic Treaty Organization and to strengthen the West's position in arms control talks by balancing off a Soviet buildup of similar medium-range weapons aimed at Western Europe.

But paradoxically the decision also has fanned the revival of the campaign against nuclear weapons in a number of central and northern European countries. Although the governments of affected NATO countries have thus far resisted pressures to withdraw support of the crucial missile decision, protecting it increasingly means containing European sentiment for unilateral nuclear disarmament.

The revival of the movement in Western Europe grows out of deepening disillusion with the escalation of the arms race between the superpowers and the stalling of arms control talks at a time of increasing East-West tension. Contributing to its development has been a greater democratization of Western European societies and an increased sense of economic and diplomatic independence from the United States within the alliance.

What directly sparked the current campaign was the disclosure in 1977 that the Carter administration was planning to produce the neutron bomb, an enhanced radiation antitank warhead that produced keen anxiety here. Then-president Jimmy Carter tabled the project in 1978, but then came public reassertion by his administration -- in a review of nuclear targeting doctrine -- of U.S. readiness to fight a tactical nuclear war in Europe if necessary.

That was followed by the NATO decision to modernize and extend the range of nuclear missiles in Europe. Subsequent scrapping of the second Strategic Arms Limitation Treaty (SALT II) by President Reagan and the U.S. Senate provided another political spur to Europe's antiatomic weapons movement.

This sentiment is commonly referred to as Europe's "pacifist" or "neutralist" tendency. These are inaccurate adjectives, actually, since most of the opposition is targeted not at the military as a whole, nor at membership in NATO, but rather at the spread of nuclear warheads. A term like "nuclear neutralism" is a more apt description.

Often senior government officials appear to have an easy but incomplete shorthand notion of what this campaign is about. During a recent week of high-level interviews in several key NATO capitals, defense officials repeatedly attributed development of the antinuclear movement to a diminished sense of the Soviet threat, particularly among European youth.

"It is a generational thing," said a senior West German defense official. "There is a lack of history among the young, especially in this country, and this results in a lack of awareness for the need for certain security policies."

In fact, though, the nuclear disarmament campaign is motivated chiefly by fear felt by old as well as young -- the fear of an East-West arms race grown out of control. A decade of negotiations intended to limit arms is seen as resulting instead in an increase in the number of atomic devices deployed on both sides.

NATO is preparing to station 572 modern U.S. cruise and Pershing II missiles in Western Europe.This means that for the first time there will be atomic warheads in Western Europe capable of reaching the Soviet Union. For some, this is seen as yet another scary dimension in the arms race.

Compounding the concern is the thought that the two superpowers may be drifting toward a tactical nuclear war limited to Europe.

A strong religious component, more Protestant than Roman Catholic, also runs through the disarmament movement, lending a moral overtone to the argument that an alternate strategy must be found to the traditional East-West nuclear deterrence. Much of the European debate about nuclear weapons takes place in churches.

"No one goes to services anymore," said the West German defense official wryly. "But the churches are central to creating the climate against nuclear weapons."

A senior British government official said he first became seriously concerned about the reborn Campaign for Nuclear Disarmament in Britian when he heard an establishment Anglican rector deliver a sermon favoring unilateral British disarmament.

The movement draws its political leadership from a mix of groups, including environmental parties seeking to broaden their voter base, youth groups and left-wing factions in Western Europe's Socialist and Social Democratic parties.

Other than the Labor Parties of Britain and the Netherlands and Belgium's Flemish Socialists, Europe's major leftist parties have refrained from moving formally into the banthe-bomb camp, preferring to hold fast, for the moment at least, to the two-track NATO decision. They do, however, put higher priority on the negotiations track which, it is hoped, will preclude the need for the new missiles.

A list of some of the roughly 30 groups planning to participate in an antinuclear weapons rally in Bonn on April 4, timed to precede a meeting here of NATO's nuclear planning group, gives an idea of who is involved:

An umbrella activist group named The Committee for Freedom, Disarmament and Cooperation, the West German environmental party The Greens, the Organization for Ecology and Peace, the German Communist Party, the Catholic and Lutheran student associations, the Democratic Lawyers' Association, and the youth organizations of West Germany's governing Social Democratic and Free Democratic Parties.

The temper of the campaign differs from country to country. In the Netherlands, where popular sentiment against nuclear weapons is strongest, the movement builds on the small-country outlook of the Dutch. Feeling insignificant in the military power play between East and West, about 60 percent of the Dutch people believe their government should unilaterally renounce nuclear weapons and thereby at least set an example for the rest of the world.

In West Germany, a powerful nation that shares a border with two Communist countries and that appreciates its pivotal role in the Atlantic alliance, the public's anxieties about nuclear weapons are similar to those in the Netherlands, but the latitude for political maneuver is generally perceived to be less.

In Britian, majority opinon still supports the Conservative government's strong commitment to NATO nuclear strategy and the basing of British and NATO nuclear weapons at locations all over the country. But the disarmament campaign has revived remarkably, attracting tens of thousands of its rallies.

Fear of nuclear conflict and left-wing opposition to nuclear missile policy also has burgeoned in NATO's Scandinavian members, Norway and Denmark, despite government policies banning nuclear weapons from their soil. This encouraged Dutch Socialists to try recently to enlist the support of Norway's governing Labor Party and Denmark's Social Democrats in a campaign opposing deployment of the new missiles in the Netherlands.