A poster-sized portrait of a Polaris nuclear missile, seen from the bottom up so as to tower in silhouette against the sky, hung on the wall of a university hall here last week as a backdrop for a conference opposing the spread of nuclear weapons.

The caption read: "Each Polaris submarine contains as much firepower as was used during World War II."

Stretched across the front of the room were black and white charts starkly depicting with stick human figures (each figure represented 200,000 real people) the number who died in two world wars and the enormously many wore who could die in a nuclear conflict: approximately 140 million in the United States, 100 million in Europe and 113 million in the Soviet Union.

"We do think war is a stupid way to settle international differences, and nuclear war borders on insanity," said retired U.S. Rear Adm. Gene R. LaRocque in an opening statement to about 150 U.S. and Europen anti-nuclear war experts and activists.

LaRocque is director of the Washington-based Center for Defense Information which, along with the Dutch University of Groningen, sponscored the conference to highlight the possibility of a nuclear war in Europe -- where Europeans increasingly fear the first nuclear bombs may fell. e

Heightened concern for the likelihood of nuclear war, spurred by the continued buildup of nuclear forces and the stagnation of East-West arms control talks, has contributed to the revival of grass-roots campaigns for nuclear disarmament in Western Europe and, to a lesser extent, in the United States. The meeting here represented a first attempt to ally U.S. and European efforts.

The immeditate aim of the campaign is to block Atlantic Alliance plans to station new U.S.-made meddium-range Pershing II and cruise nuclear missiles in Europe beginning late in 1983 -- a move deemed necessary by Western officials to offset a buildup of Soviet SS20 missiles.

Opposition to the modernization plan is keenest in the Netherlands. The Dutch Labor Party, the country's largest political party, is trying to get back into government in national elections next month by running on a platform that rejects a Western request that the Netherlands take 48 of the 572 planned new missiles.

Conference organizers said the meeting's timing and its location in the Netherlands had not been intended to influence the election outcome. But U.S. and NATO officials declined invitations to attend, possibly to avoid the appearance of official sanction.

"In preparing for this conference," LaRocque said wryly, "we got the distinct impression that the [NATO] nuclear planning group would have preferred we delayed holding it, perhaps until after the war."

Several panels of military and scientific experts offered what amounted to an information base for a movement that is often regarded by Western government officials as being uninformed and overly emotional in its arguments.The two-day meeting was billed as the first authoritative public disussion in Europe of the chances and effects of a nuclear war.

Yet while all were in agreement on the need for action, the conferees disagreed on how to try to reverse what was generally seen as a world drift toward nuclear war.

The argument outlined here is this: The traditional strategy of nuclear deterrence has led to a sustained arms race.Arms limitation talks have failed. Moreover, Western governments have come to accept the notion that a nuclear war could be limited to certain targets or regions. To this end, they are developing more accurate weapons across a more flexible range of options.

But such developments, say the antinuclear campaigners, only increase the risk of the firing of an atomic weapon. In fact, they say, nuclear war could not be contained or controlled once it broke out and would inevitably result in immense destruction.

Western officials argue that deterrence strategy and a mutual East-West arms buildup has at least had the advantage of providing 35 years of relative world peace. Rejecting this, Gronigen Prof. Hylke Tromp quipped, "If you have jumped from the Empire State Building and are passing the 35th floor, you can't say you are flying."

The explosive and radioactive effects of nuclear explosions were described in gruesome detail -- an exercise in what Herbert Scoville, former deputy director of the Central Intelligence Agency, termed "consciousness raising."

But the doomsday imagery seemed only to deepen what one after another who rose from the audience described variously as despair, helplessness and pessimism about the nuclear threat. Bernhard Benson, a writer who lives in Paris, said the world today is divided between "the four billion who don't want to fry and the 200 playing international chess" with nuclear weapons, though these 200. Benson added, may not be happy with the situation either.

Although the Soviets' recently gained nuclear superiority in Europe was noted, Western plans to station new nuclear missiles in Europe were seen as another dangerous step in the arms race. The problem for the peace movement was presented as how to block NATO deployment without doing political damage to the alliance.

This drew differences. The major campaign groups -- the Interchurch Peace Council in the Netherlands, the Campaign for Nuclear Disarmament in Britain, the environmental "Green Party" and Campaign for Atonement and Peace in West Germany -- favor unilateral renunciation of nuclear weapons by smaller European countries in hopes this will influence the major powers to negotiate limitations on their weapons. They also are pressing for the declaration of nuclear-free zones in Scandinavia or southeast Europe and talk vaguely about developing some form of exchange between Western Europe's peace movement and the movements for civil, intellectual and trade union rights in communist Eastern Europel.

But unilateral moves are seen by a minority within the peace movement as upsetting alliance solidarity and particularly endangering the pivotal but delicately balanced leadership of West German Chancellor Helmut Schmidt. This group would rather stay with a multilateral approach and would urge NATO to reconsider its missile modernization decision in light of growing opposition -- a possibility recognized here as slim given the current outlook of the Reagan administration.