HARDLY anyone ever reads the platforms of the Republican and Democratic Parties - especially those produced at midterm conventions. Leaders often spend as much time repudiating their parties' positions as conforming to them. Not so in Britain, where the party manifesto is cut in stone and is a reasonable - though not resolute - road map to the way ahead. For that reason, the position on defense and security recently adopted by the annual Labour Party Conference cannot be lightly dismissed.
In summary, the Labour Party wants to restructure Britain's defense policy from the ground up. Its Polaris and Trident submarines - the so-called independent nuclear deterrent - would go. The United States missile-carrying submarines based at Holy Loch in Scotland would go, along with US F-111 bombers that can carry nuclear weapons. And so would the US cruise missiles so painstakingly installed in Britain following four years of divisive debate within the North Atlantic Treaty Organization. Britain's contribution to Europe's conventional defense would remain, but with hardly a farthing more to support it than today.
It is possible to discount much of this as an excursion of a party with precious little hope of returning to power after the massive victory of Prime Minister Margaret Thatcher's Tories following the Falklands war, with the challenge from a new centrist party (the Social Democrats), and with the major shift leftward in Labour politics. Nor can the fateful steps necessarily be counted on if Labour comes to power when the next elections take place three or four years from now: Prime Minister Harold Wilson did defy his party in 1964 when he retained the Polaris missiles provided for in the Nassau Agreement with the US.
But what if a Labour government did throw all the nuclear weapons overboard? For our part, we would have little difficulty with the disappearance of Britain's own nuclear weapons. We have always been ambivalent about them, and their departure would somewhat simplify US-Soviet arms control talks over European-based nuclear weapons. With the impending deployment of new US Trident submarines and their long-range missiles, the US base at Holy Loch will in any event become expendable, and the F-111s could probably find homes somewhere on the Continent.
The cruise missiles are the nub of the problem. Given the political complexities of the whole issue of NATO's intermediate-range nuclear forces (INF), Britain's opting out would intensify public pressures in Holland and Belgium to forestall their accepting similar weapons. The brutal debate in West Germany over INF weapons, which dominated allied debate in 1982-83, would be rekindled with a vengeance.
Allied governments, however, usually have ways of meeting problems when they are convinced that serious matters are afoot. In the absence of an INF arms control agreement with the Soviet Union by the time Labour acted, the West German government would want to cleave even more closely to the US. It would either define the threat from Soviet SS-20 missiles as being less serious than thought now, or it would grit its teeth and try to soldier on with INF deployments on its own soil. The French - with allusions to Albion perfide - would step up military cooperation with West Germany. And the Italians might take the opportunity to prove they are better allies than the British.
Even if all this worked, however - and it would be a close-run thing - something else would be clear: Britain would be effectively isolated from the Continent. Nuclear weapons are deployed in Europe now only in part to deter war: along with conventional forces, they also testify to the sharing of risks among allied countries on behalf of NATO's overall security and resilience against Soviet political inroads. Unless the British Army of the Rhine were increased substantially - where the Labour Party places undue emphasis on quality rather than quantity - the United Kingdom would be viewed as no longer a part of Europe. Its influence in the European Community would drop to zero.
That any of this could come to pass must now seem like fantasy. But the Labour Party's action does indicate how deep are the roots of concern in Britain - and also elsewhere in Europe - over the vexed question of nuclear weapons in NATO's stragegy. It is a first glimmer that the INF issue has not been laid to rest but rather has only enjoyed a respite after last year's exhausting political combat.
This lesson needs to be taken aboard by the Reagan administration. The Soviet Union snookered itself when it walked out of the INF talks last November, just before the first NATO missiles were deployed; there is now more understanding in Western Europe of Moscow's share of responsibility for the failure of arms control. But the political benefits of this realization are likely to be limited , unless we are able to follow up on the arms control rhetoric of President Ronald Reagan and the Soviet-American agreement to ''keep in touch'' after the visit to Washington of Soviet Foreign Minister Andrei Gromyko.
As misguided as the Labour Party's discussion of Britain's role in Western defense may be, it has done the alliance one favor: It has reminded all concerned that emotionally charged and politically difficult issues of nuclear weapons cannot be left to take care of themselves.