Britain: no change in course

Britain is not changing course because it has lost a destroyer, a jump-jet, and some 31 men in the South Atlantic. Its diplomacy will continue to be backed up by force where necessary.

The total exclusion zone around the Falkland Islands will be enforced and no future actions are ruled out.

That is the message from the British government as the entire nation takes stock of the new situation in the war zone now that Britain has suffered its first major losses.

Alarmed opposition to Britain's own use of force mounts at home and in Western Europe, but government backbenchers here are adamant: ''Our cause is right,'' says the chairman of the largest backbench committee, Edward Du Cann.

''Attacks on air bases on the Argentine mainland cannot be ruled out,'' he said.

The destroyer Sheffield was set on fire and disabled by a deadly Exocet sea-skimming missile from a French-built Super Etendard fighter-bomber thought to have been based at Rio Gallegos.

Clearly, more British ships are now vulnerable to the Exocet missile. According to Jane's Weapon Systems, a standard reference guide, the missile has a range of 28 nautical miles when fired from the air and 20 nautical miles from a ship.

''I hate to see people die, but how can we give in now?'' asked an anguished, well-to-do woman in London's affluent southern suburbs. ''I would not want our forces to seek out Argentine ships or planes, but if they try to get through to the Falklands, well, yes, I suppose we have to stop them. Otherwise, dictatorship will have won. . . .''

The opposite view came from a young woman on a London city street: ''What a waste,'' she snapped when asked about the loss of the destroyer. ''We should agree to talk now. There will be a diplomatic settlement in the end anyway.''

British officials say that Argentina must not be allowed to stay on the Falklands, which it seized April 2, using diplomatic maneuvering as an excuse to hang on to occupied territory.

For that reason, Britain intends to reject any United Nations or other call for a cease-fire or truce until Argentina at least agrees to withdraw.

The British task force will not pull back, even a short way, until London is guaranteed that Argentine forces are withdrawing.

If Argentina does leave, no diplomatic options are ruled out here: joint interim administration supervised by the United States or the UN, sovereignty going to Argentina at an agreed time provided the islanders can choose their own way of life, or perhaps even United Nations' trusteeship.

This overall strategy, indicated by the Foreign Office May 5, lay behind two reports to the House of Commons on the same day, one by Defense Secretary John Nott and the other by Foreign Secretary Francis Pym.

Britain was reported not to be in favor of an immediate Security Council meeting in New York in the immediate aftermath of the sinking of the cruiser General Belgrano and the disabling of the Sheffield, although Mr. Pym said he was in constant touch with UN Secretary-General Javier Perez de Cuellar.

At this writing British officials did not deny but said they had no knowledge of ''a major'' naval battle around the islands, as reported by American intelligence.

It was clear, however, that British task force commanders remained under orders to enforce the air and sea blockade and that meant shooting to kill if the zone was breached or the task force itself was in danger.

Meanwhile, Prime Minister Margaret Thatcher continues, at least in the short term, to be able to prosecute her diplomatic, military, and economic strategy.

Although some of her remarks have left the impression that she's relying now more on force than diplomacy, Mr. Pym continues to assure the House that the best hope of a settlement still lies with US Secretary of State Alexander M. Haig Jr.

Mr. Pym said May 5 he had contributed ideas, along with the government of Peru, to Mr. Haig, and was also responding to the UN Secretary-General's ''ideas.''

It was clear May 5, however, that London held out no real hope for an early breakthrough and put the blame squarely on Argentina.

Mrs. Thatcher has a large majority in the House of Commons, and the bulk of her own party stoutly supports her so far. Voices such as former leader of the House Norman St. John-Stevas, urging no more escalation but intensified diplomacy, appear in the minority.

Senior Labour opposition spokesmen also demand that Argentina must withdraw, but they place more emphasis on the United Nations than the government seems willing to venture.

Elsewhere in the Labour Party, opinion is widely split, mirroring the concern and apprehension in the country as a whole.

Labour Defense spokesman Stanley Clinton Davis calls for ''graduated and proportional'' use of British force. Further to the left, 70 Labour members of Parliament have tabled a Commons' motion demanding an immediate truce. On the far left former minister Tony Benn calls for an immediate cease-fire, saying: ''We must stop the killing now.''

Social Democratic parliamentary leader David Owen, a former foreign secretary , suggests UN trusteeship for the Falklands, and Liberal leader David Steel supports new efforts at diplomacy.

On naval tactics the Labour Party believes that sinking the cruiser General Belgrano violated government policy of using ''the minimum force necessary.'' Labour spokesman Denis Healey keeps on asking Mr. Nott how far the cruiser was from the British task force when attacked. Mr. Nott has refused to reply on security grounds. Mr. Nott revealed May 5 that the decision to fire two torpedoes was taken by the submarine commander but was fully justified by the rules of engagement imposed by the government.

There is considerable concern here that naval warfare might take on a momentum of its own and that many more lives may be lost on both sides unless some face-saving solution can be quickly found.

Even if British commanders are ordered to fire only in self-defense, they showed by sinking the General Belgrano that they are able to attack enemy ships outside the enemy exclusion zone. The Belgrano was 35 miles from it.

The conservative military lobby is also asking why the task force was unable to stop the Exocet missile from hitting the Sheffield. Neither Harrier jets, electronic countermeasures, nor the Sheffield's own weapons detected the incoming missile.

Nine Argentine ships carry the Exocet, it is reported here, including the two destroyers that were allowed to escape while escorting the General Belgrano. British ships carry the same missile, but only two British frigates possess the Seawolf antimissile-missile designed to counter it.