As the uproar over the Grenadian expedition mounted, you could take your choice among the legal eagles who claim that the United States has done all sorts of violence to the norms of law, domestic and international. The ancient maxim was "inter armes leges silent" (amid the clash of arms the laws grow quiet). But nowadays the barest whiff of gunpowder anywhere brings on a talkfest of legalism.

To the usual worries--starting with that old bugaboo, the Rio Treaty, last heard of during the Falklands War--a novelty has been added: the danger that President Reagan's sudden, decisive action in the Windward Islands infringes the prerogatives of Her Majesty, Elizabeth II. As head of the British Commonwealth, she is through her governor general, Sir Paul Scoon, the titular sovereign of Grenada. And any partisan use of Scoon in the restoration of legitimate authority on the island would violate constitutional rules.

Now, I am the last to wish any legal insult to a great lady. But the worry over the fine points of constitutionality when, in fact, Sir Paul Scoon had been under house arrest and perhaps in mortal danger, seems perfectly symptomatic of the problem. We live in a world whose vast majority are ruled by brute force, and where law proceeds in most places from the barrel of somebody's gun. That was certainly the situation in Grenada until Tuesday morning.

Where the new world differs from the old is in the cynical tendency to invoke law any time free and lawful societies combine to resist thuggish mischief. In Grenada, in addition to the danger that several hundred young Americans might be captured or even murdered, we had seen the government of Maurice Bishop overthrown, Bishop himself murdered (probably for seeking better relations with the Unitd States), and the Cubans on the verge of becoming the only force sufficient to control events. If that did not point Grenada toward satellitedom, it certainly made a mockery of the Queen's titular authority.

The more imaginative interpreters of the international scene claim that the invasion of Grenada establishes a Reagan version of the Brezhnev doctrine. The absurdity of that view will soon be tested. For either there will be an election in Grenada under regional sponsorship, or there will not. Either the Grenadians will be free to choose a new government or they will not. And either the constitutional processes bequeathed to Grenada by the British will be observed or they will not. And if any of this happens in Grenada, it will be far more than has happened since 1968 in Czechoslovakia, or since 1979 in Afghanistan.

All the Grenadian operation has in common with recent Soviet enforcements of the Brezhnev doctrine, so-called, is the unpleasant use of military force. If force per se is to be condemned, if the legitimacy of its use under international law has nothing to do with intent or result, then it is anarchy merely disguised as law. And if you seek a precedent for that kind of law, think of the 18th Amendment and Prohibition.