TSUPERFICIALLY, there is an Alec Guinness quality to Argentina's takeover of Britain's tiny, remote Falkland Islands in the South Atlantic. But it is a serious affair, and it could have grievous consequences--for Argentina--if the regime in Buenos Aires does not quickly end its foolish venture and restore the status quo.

It is clear enough why Argentina, having for 149 years kept within bounds its outrage over Britain's hold on the Falklands, invaded early Friday. It was no case of a nation's being finally provoked beyond all human tolerance by some new injustice or humiliation. Nothing whatever had happened in the Falklands, whose 1,800 inhabitants have repeatedly opted to stay with Britain. But something had happened in Argentina. As part of the bargaining within the armed forces that recently produced a new president, nationalistic elements in the officer corps gained a new ascendancy. The economic program of the government is increasingly unpopular. A distraction was considered timely, and so the army moved, knowing that all Argentines, regardless of their current political views, are brought up believing that the Falklands are the Malvinas.

Britain's prime minister spoke the simple truth when she labeled the Argentine act "unprovoked aggression." It is more than likely that the Argentines have made a serious mistake by taking advantage of Britain's distance and inattention. For Mrs. Thatcher is a tough woman, not inclined to let British subjects be run off a part of the British range, and the British do not appear to be in a mood to be pushed around. The Brits have nothing to apologize for in the Falklands. Mrs. Thatcher's government is taking the case to the United Nations--and dispatching a 40-ship fleet.

Did the Argentines think that, with the administration deciding to resume arms sales and seeking their hand in Central America, they could get the president to wink at their grab of the Falklands? We trust Mr. Reagan left no doubt of the American rejection of the grab when he tried to talk President Galtieri out of it on Thursday. Argentina committed aggression. By doing so it removes itself from consideration as an American partner in other hemispheric matters. Perhaps the Argentines will think of that when their collective head clears.

Up at the United Nations yesterday, the Security Council gave pretty much the sort of shoddy performance that has brought the world body into disrepute over the years. Only 10 of its members could bring themselves to demand an immediate Argentine pullout. Panama gave full aid and comfort to the aggressor by opposing the resolution, and the Soviet Union and China, with Poland and Spain, gave almost full aid and comfort by abstaining. It will be interesting to see how these governments square their support of Argentina's acquisition of territory by force with, for instance, their denunciation of the Israeli position in the West Bank. Perhaps the United Nations is so far gone as a political institution that it is foolish to tax it with a demand for consistency, or to point out that its credibility--its remaining credibility--is at stake.