There was a clear storm warning for the United States in that swelling, adrenal rumble of "hear, hear!" in the House of Commons, as Prime Minister Margaret Thatcher proudly proclaimed for the Battle of the Falklands roughly what Robert Southey wrote of the Battle of Blenheim: "'Twas a famous victory." Only a few opposition churls saw fit to ask the question that Southey couldn't answer: "But what good came of it at last?"

The Thatcher government thinks it's obvious: "Aggression" has been punished, freedom served. So now it will fortify the Falklands, garrison them with three times as many troops as there are islanders to defend, develop their economy, maybe grant them independence. But never, never again will Britain entertain the risk of negotiations that might wind up conceding ultimate Argentine sovereignty (as earlier negotiations did).

Well, that line may do for the British and for Thatcher's immediate political imperatives. But what it does for the United States is best captured by the suggestion from some British quarters that American troops would fit nicely into some future Falklands "peace-keeping" force.

What that says is that the British think the United States has somehow signed on for the duration, not just of the British effort to regain the islands but for however long the British choose to sit there, refusing to discuss the issue of ownership.

It's understandable. The Reagan administration has been remarkably sloppy about the way it has expressed its "support for Britain." There has been altogether too much sentimental talk about special relations and old friendship and not nearly enough strict adherence to the narrow point of principle at stake: the unacceptability of a resort to force to settle international disputes.

Small wonder, then, that U.S. support for the U.N. resolution requiring Argentine withdrawal --and for Britain as the only available enforcer of that resolution--is in danger of subtle transformation by the British. One senses an expectation by the British of at least implicit, open- ended American sympathy for their side of the sovereignty argument.

How else can you interpret the new and insidious British suggestion that the Falklands are not just a bleak sheep farm but, all of a sudden, a vital strategic asset, crucial to Alliance interests, a veritable foxhole for freedom, to protect South Atlantic sea-lanes in case the Panama Canal is closed?

To this line, there is only one safe and sound response. Where the administration has been effusive, it must now be precise. American relations and interests in this hemisphere have already been sufficiently damaged by the Falklands affair. The damage can only be compounded and the American conflict of interest prolonged by even the appearance of U.S. support for a stand-pat British position on the sovereignty issue.

Worse, by failing to pressure the British for flexibility on the question of future negotiations, the United States could be making its own contribution to the very real possibility of another Argentine resort to force.

The U.S. Ambassador to the United Nations, Jeane Kirkpatrick, may have put a foot wrong here or there in the Falklands affair, but by the end of it she had the perspective just right. The Argentine "possession" of the islands was Phase One, as she saw it. Even before the Argentine surrender, she was saying that a British victory would simply end Phase Two. "But that only brings us to Phase Three," she added. "I think we must be very clear that the British repossession of the islands doesn't necessarily mean the end of this war."

According to this theory, shared by others in the Reagan foreign-policy apparatus, it doesn't matter whether the present Argentine junta survives, or by what it is replaced. The war has wildly inflamed "Malvinas" fever; any ruler of Argentina will have to play to it.

A conciliatory British policy won't necessarily bring a settlement. The Argentine capacity for miscalculation, if the recent record says anything, is limitless. But British rigidity will only make it easier for the Argentines to justify doing what is predictable: massive rearmament with more sophisticated weaponry.

The lesson for Argentina is not likely to be that aggression doesn't pay--only that it doesn't pay when you are outgunned.

The heavy cost in blood and treasure does not argue well, with British public opinion, for yielding up what was so hard-earned. For the Reagan administration, the choice is easier.

Granted the need for time to let tempers cool. But the interest of the United States in rebuilding relations in the hemisphere cannot be met by a de facto resolution of the Falklands- Malvinas dispute, by force of arms to Britain's satisfaction. It will require a concentrated effort to bring about a negotiated settlement to the satisfaction of all concerned.