British Labour vote tests NATO. West Europe's left is restive. Opposition parties are urging cuts in or elimination of nuclear forces. NATO is worried, but some see opportunities for new alliance.

The British Labour Party's decision to say, in effect, ``out'' to all nuclear weapons -- British and American -- has profound implications for the Western alliance. Yesterday's vote by party members to officially adopt a policy of unilateral nuclear disarmament puts a large question mark over the two fundamental planks in British foreign policy since World War II: Anglo-American defense cooperation and Britain's commitment to NATO.

Critics of Labour's new unambiguous stance charge that, if Britishers vote in a Labour government in the next election, its policy will upset the balance of forces in Europe and violate Britain's vital defense agreements with its NATO partners.

In a highly publicized television interview, Caspar Weinberger, the US secretary of defense, blasted Labour's defense policies as undermining NATO.

US Ambassador Charles Price II, a conspicuous figure at the party's conference here at this Lancashire seaside resort, drove home the point that Mr. Weinberger, contrary to Labour's assertions, was speaking for the Reagan administration. Ambassador Price also added a warning that if the US had to pull its nuclear forces out of Britain, it might also have to think about taking out its 29,000 military personnel now stationed here.

That, in turn, has aroused concern among defense strategists that isolationist senti ment in the US might be encouraged and would intensify demands in the US to bring back all of its nearly 350,000 troops stationed in Europe.

If Britain were to forgo its nuclear capability, it would leave only France, not a fully militarily integrated member of NATO, as the sole European member of the Western alliance with its own independent nuclear deterrent.

There is also speculation that if Britain, under a new Labour government, were to get the US cruise missiles off British soil, it would put enormous pressure on Belgium and the Netherlands to follow suit. Both countries faced stiff public opposition to cruise deployment.

What particularly worries the Americans is that Britain is poised for a general election within the next year and a half. At the moment, Labour has brushed aside the challenge of the allied Social Democratic-Liberal Parties and has established itself as the principal opposition party in Britain.

Labour has also consistently been ahead of the ruling Conservatives in the polls in recent months.

Under a Labour government, Britain would:

Remove Britain's current independent nuclear deterrent, the Polaris submarines.

Cancel the new and more sophisticated deterrent, the sub-launched Trident nuclear missiles.

Remove cruise missiles and close down all US nuclear bases including Holy Loch in Scotland, at present the only base in Europe for America's Poseidon nuclear submarine.

Prevent F-111 fighter planes, which can be equipped with both nuclear and conventional bombs, from carrying nuclear weapons.

Stripped of its nuclear component, Labour insists, Britain will still remain a member of NATO, while maintaining and strengthening its conventional forces.

Labour is opposed to Trident not just for ideological reasons. The party also feels the 9 billion to 10 billion ($6 billion to $7 billion) that Trident will cost could be better spent on boosting British conventional forces. This, Labour defense spokesmen maintain, would help balance the numerical advantage now enjoyed by the Warsaw Pact.

But Conservative Defense Minister George Younger has argued that even if every penny saved on canceling Trident went to conventional forces, it still would not provide a credible deterrent. And, he insists, the stationing of Euromissiles has been a major success for the British government's policy of standing firm, and that this will eventually force the Soviets back to the negotiating table.

Labour's disarmament policy, while enthusiastically upheld at the party conference here, has some detractors within Labour's own ranks. Some members of the party -- many of them expected to become cabinet members should Labour become the ruling party -- reportedly have real concerns about what they see as fulfilling existing obligations.

The pro-Labour newspaper, the Mirror, while giving a glowing tribute to party leader Neil Kinnock, said in an editorial that it ``does not agree with Mr. Kinnock's defense policy.'' Two of the paper's well-known columnists were equally critical.

One middle-of-the-road Labour member of Parliament described the vote as ``disastrous.'' He said, ``The party, frankly, is neutralist, but hasn't the guts to accept the logical outcome of its policy.''

However, Nicholas Raynford, the newest Labour MP, maintains that his party's new disarmament policy will succeed where it failed in the the 1983 elections. The party is now more unified, in part because of the Chernobyl factor, and Mr. Raynford does not think the Labour Party would again make the mistake of appearing pacifist.

One of the significant ironies of this party conference season as a general election draws closer is that the domination of defense issues has pushed unemployment, education, and social services -- issues on which the government is distinctly vulnerable -- into the background.

The result is that the Conservatives will now plug defense, an area in which they have historically been more successful than other parties in turning to their own political advantage.

The war with Argentina over the Falkland Islands in the spring of 1982 was a case in point.