This appears to be a climactic week in the Falklands conflict. The question is whether Britain will lose patience in diplomacy and step up its military pressures to the point of a major invasion. Or whether it will have the political fortitude to see the diplomatic effort through. Everyone must hope and pray that it will choose the latter course. The United Nations quest for a solution would preserve the moral and legal principle on which the British have taken a stand even while satisfying Argentina's concerns.
Prime Minister Margaret Thatcher must weigh carefully the cost of more fighting. In human terms alone the price is high. As operations so far have painfully shown, Argentina's access to modern-day missiles puts every British ship in jeopardy; few think a landing on the Falklands could be accomplished without further loss of life. Military escalation in this day and age carries with it heavy risks.
Then there is the diplomatic cost. The longer armed hostilities go on and the more virulent the battle, the more difficult it will become for diplomacy to separate the combatants. In the end, they still will have to come around to a negotiated settlement. In the meantime, considerable diplomatic damage already has been done: London's relations with its Common Market partners have been ruffled, as illustrated in the controversy over sanctions.Washington's ties with Latin America have suffered profound strain from which it will be difficult to recover if the crisis boils on. The Soviet Union, for its part, has managed to put its propaganda oar in and cannot but be delighted at the new opportunity for extending its influence in the Western hemisphere.
This is not to impugn Britain's policy of holding firm to a matter of principle. Britain has amply demonstrated its willingness and determination to do so, and advocates of world law and order can only be grateful for this. The principle of nonaggression is being upheld. But it now must be asked whether wisdom does not call for the kind of settlement which UN Secretary-General Javier Perez de Cuellar is trying hard to achieve. The UN plan is based on the diplomatic imperative that each side must emerge being able to claim it has won something. In other words, ''no winners, no losers'' -- a face-saving formula often employed in nasty disputes of this kind. In essence the UN proposal calls for a cease-fire, a simultaneous withdrawal of forces, a temporary UN administration over the islands, and negotiations on the question of sovereignty.
To their credit, both sides have eased their original positions considerably. Argentina does not demand explicit British recognition of its sovereignty; Britain no longer insists the inhabitants of the Falklands be allowed to determine the future of the islands. Having come so far, it ought to be possible to go the distance.How tragic if nationalistic pride and mutual distrust clouded sensible judgment and postponed what ultimately must still be a negotiated solution under which the status of the islands is changed.
To cajole the parties to come to agreement is not only Mr. Perez de Cuellar's delicate task. US diplomacy should continue to lend a hand, both by firmly nudging the Thatcher government and by showing more overt support for the UN's efforts than it has so far.
In recent years it has become fashionable to downgrade the United Nations as a bumbling, ineffective peacemaker. Indeed its limitations are all too evident. But unthinking cynicism does the UN an injustice. On some occasions -- in the Middle East, for example -- the UN has proved helpful, and this could well be another such time. When two nations are on the brink of full-scale armed conflict -- a war with dangerous military, strategic, and political implications -- should not every avenue of peaceful accommodation be explored and wholeheartedly backed? It does Washington no credit to appear the bystander as Mr. Perez de Cuellar works discreetly behind the scenes to bring about peace.
This is, in short, a moment for sober calculation and restraint in London and Buenos Aires. There perhaps is always a risk of delay or disappointment in opting for peaceful diplomacy rather than war. But the dangers of war are surely far greater.