Britain's opposition Labor Party formally pledged today to adopt a "nuclear-free defense policy" including the immediate rejection of all cruise missiles and the ouster of American bases should the party lead the country's next government.

In a sweeping "campaign document" that represents Labor's official positions on both foreign and domestic issues, the party committed itself to withdrawal from the European Community and said it would adopt "a massive program" of public spending to curb unemployment.

The document confirms that Labor will go into the coming election, which many here expect to take place later this year, on a radical platform that--if implemented--would fundamentally transform Britain's role in the world. In particular, relations with the United States and continental Europe, cornerstone of the country's foreign policy, would be dramatically recast. Labor is still far and away Britain's second largest party in Parliament and although trailing the ruling Conservatives in polls, it remains a contender for recapturing a majority.

The program has been drafted in prolonged bargaining among Labor's leadership and is intended to offer voters an unequivocal summary of what the party would do. The 15,000-word text becomes the party's doctrine from which its manifesto will be drawn whenever a national election is called.

Defense policy proved to be the most contentious issue. Labor's leader, Michael Foot, has long favored unilateral nuclear disarmament and at the party's annual conference last fall, delegates overwhelmingly supported his stand. Nonetheless, such party stalwarts as Deputy Leader Denis Healey clearly favored much less drastic steps.

The Foot position prevailed, with the only concessions being a promise of "maintaining cooperation with our allies" and fixing the date for nuclear disarmament as during the "lifetime of the next Parliament," a period of five years. The document envisions Britain remaining in NATO but says the alliance should "develop a nonnuclear strategy."

While promising to reduce overall defense spending, the document says Britain should have "sufficient military strength to discourage external aggression." There is specifically no mention of upgrading conventional forces.

Under its "emergency program" for the government's initial days, the party pledges to refuse deployment of cruise missiles, order any in place to be removed and cancel Britain's purchase of U.S. Trident submarines, the basis of the country's future nuclear deterrent.

Under its longer-term plans, Labor is committed to "removal of all existing nuclear bases and weapons, thus enabling us to make a direct contribution to an eventually much wider nuclear-free zone in Europe. However, all this cannot be done at once, and the way we do it must be designed to assist in the task to which we are also committed--securing nuclear disarmament agreements with other countries and maintaining cooperation with our allies."

On the European Community, another issue that has divided Labor in the past, the party asserts that it will begin the process of disengagement as soon as it takes office.

At home, the party's approach would mean a similarly major reversal of strategy from its present direction, using expansionary economic means of curbing unemployment.