Two public declarations this week--a speech by the secretary of state and an article by four senior officials of previous administrations--could provide the basis and focal point for one of the most important debates on American nuclear policy in years.

The speech by Alexander M. Haig Jr. and the article--written by McGeorge Bundy, Robert S. McNamara, George F. Kennan and Gerard Smith--represent well- News Analysis News Analysis crafted arguments on opposing sides of a central question stirring populations here and abroad. That question: How best to continue avoiding nuclear war?

Linked to that question in this week's debate is another of only slightly lesser importance: How best to preserve the unity of the Atlantic alliance and to influence the future course of the most important military and economic ally of the United States on the Continent, West Germany?

Haig's view is that nuclear deterrence is essential and that preserving the threat of the first use of atomic weapons in Europe to prevent a Soviet onslaught by numerically superior conventional forces is essential to that deterrence.

The four officials argue that the vast proliferation of atomic weapons on both sides makes that threat no longer credible and opens the world up to potential nuclear catastrophe.

They call for a major study to see if renouncing that first-use threat is not a wiser path.

The reason West Germany is so crucial to this difference of view is that it has basically entrusted its defense since the end of World War II to the American nuclear shield.

Haig argues that the time-tested policies of the past 30 years, supported by every American administration and the North Atlantic Treaty Organization, have preserved the peace in Europe and prevented a clash between the superpowers. Dropping the first-use threat, Haig maintains, would be tantamount to inviting the Soviets to invade. And, he adds, critics who oppose reliance on nuclear weapons are no more moral than those who seek to maintain peace through continued nuclear deterrence.

To those who want to freeze nuclear forces at a level that he believes would favor Moscow or to abandon the first-use threat, Haig says "the stakes are too great and the consequences of error too catastrophic to exchange deterrence for a leap into the unknown."

The four former officials do not dispute the concept of military balance or deterrence. But they have put their prestigious fingers on the single, most likely flash-point for nuclear war--the murky doctrine that would allow the West to be the first users of atomic weapons on a European battlefield.

The officials argue that there are no conditions that could justify being the first to set off what they and a number of other specialists believe would ultimately become an uncontrolled nuclear holocaust fed by 50,000 atomic weapons in the combined superpower arsenals.

The officials maintain that the nuclear issue is so contentious and frightening in Europe that doing away with first use--though retaining the pledge to respond with nuclear weapons if the Soviets use them first--would improve alliance unity and provide the basis for strengthening of conventional forces so that the Soviets remain deterred from attacking.

Bundy, the former national security adviser to presidents Kennedy and Johnson, argues that a prosperous Western Europe can afford it, and that it would be quite a bargain if it would be a step back from the nuclear threshold.

The co-authors of the no-first-use proposal are also well-known figures. McNamara was secretary of defense for seven years in the Kennedy-Johnson administrations. Kennan, a former ambassador to Moscow, is one of the country's elder statesmen, and Smith led the U.S. negotiating team under President Nixon that worked out the first strategic arms control agreement with the Soviets.

Nevertheless, because they are tampering with a serious issue and longstanding policy, the authors face an uphill battle. Kennan and Smith have been known for years as having serious doubts about the first-use policy. But McNamara and Bundy were part of administrations that helped boost U.S. nuclear weapons in Europe and committed U.S. military power to Vietnam. While they argue that things have changed drastically since the 1960s, their past associations rather than the new proposal could attract the attention of critics.

European reaction to their proposal will be a crucial test.

Will Europeans fear that withdrawal of the first-use threat uncouples them from the broader American nuclear umbrella that has been held protectively over the alliance since the end of World War II?

England and France are sovereign countries with their own nuclear weapons. Would France forgo their use if they were in danger of being overrun or even if their neighbor, West Germany, was about to collapse?

Would such a move tempt West Germany to develop its own nuclear weapons? Would it weaken pro-alliance forces in West Germany and force Bonn into being more accommodating toward the Soviet Union, a disturbing trend that some in the West claim to see already?

Does anybody in Central Europe want West Germany to have a bigger army?

Is there any reason to believe Western Europe would hike defense budgets and increase its armed forces to add the necessary strength?

Would it mean, as Haig suggests, a return to the draft in this country, or is the secretary just trying to cool the ardor of anti-nuclear forces by suggesting that their sons may be drafted if we drop the first-use threat?

The Polish crisis has provided a dramatic example of the weaknesses within the Soviet Bloc, but would only a conventional western defense deter the Soviets?

The authors do not claim they have these answers and want a major study undertaken to try and find some. They have company in the form of some other conservative intellectuals and former senior military commanders who also view the first-use concept as dangerously flawed.

It has been almost 20 years since the Cuban missile crisis, when Americans were forced to look hard into the abyss of nuclear war.

As Haig said in his speech: "It is right that each succeeding generation should question anew the manner in which its leaders exercise such awesome responsibilities. It is right that each new administration should have to confront the awful dilemmas posed by the possession of nuclear weapons. It is right that our nuclear strategy should be exposed to continuous examination."