London — They are saying here in Westminster that if things were not to work out right for Margaret Thatcher and Great Britain over the Falkland Islands the United States would find its European alliance in tatters.
Britain's Trident missile would be scrapped. (It may be anyway). Polaris would be phased out. Britain might withdraw from the European Community and possibly even NATO.
These things could happen, not because of some vengeful reaction but because Labour could surf into power on a great wave of disappointment with and even rejection of the Tories.
Even if there is a relatively successful outcome to the crisis from Mrs. Thatcher's point of view the future of Trident is in doubt.
You will find very few people indeed in Britain who agree with the policy of running down the Royal Navy which the Thatcher government embarked upon. The task force heading for the South Atlantic is led by one aircraft carrier that has been sold to another country already and another scheduled for the scrapheap.
To most armchair strategists one of the lessons of this crisis is that for an island the navy really is the senior service and must always be treated as such.
A second lesson, hard as it my sound, is said to be that you should not hang on to possessions you cannot defend, particularly in a world full of dictators, military goverments, and anti-western feeling. No person I have spoken to believes that the Falkland Islanders will wish to remain in their islands even if the Argentine armed forces are expelled or withdrawn.
Yet of course the world cannot be run once again on the principle that might is right and that the United Nations can be flouted with impunity. That way lies chaos, war, and, with the nuclear weapon always in readiness, possible obliteration.
Therefore a relatively successful outcome for Margaret Thatcher and Great Britain is vital to both superpowers, but particularly to the US.
I say ''relatively successful'' because total success for Britain appears beyond the bounds of possibility. If Argentina is brought to understand this and to behave now with honor rather than shame, a naval action which could have unthinkable repercussions could be avoided.