London — Believing that Argentina has its ''back to the wall,'' a confident Britain is piling on the pressure around the Falkland Islands while naval strategists here plan their next moves.
Part of the pressure is immediate and physical: using air and submarine power. Britain said it sank one armed Argentine naval auxiliary ship and damaged another May 3 just a few hours after one of its nuclear submarines ''severely'' damaged the cruiser General Belgrano with torpedoes.
British strategy is to inflict damage that is spectacular but does not kill indiscriminately. Two escort ships believed to be frigates with the General Belgrano were allowed to escape unharmed.
Another part of the pressure is long term: the requisitioning of four more ships, including the cruise liner Queen Elizabeth 2, and the alerting of an extra infantry brigade to stand by to be shipped to the war zone. The brigade could include as many as 3,000 men.
The requisitioning of civilian ships over the past three weeks is in part designed to force Argentina to face the fact that London is prepared to keep on fighting for months, if necessary, to isolate the Falklands and force the occupying Argentine troops to withdraw.
A third part of the pressure is psychological: using the short-wave World Service of the British Broadcasting Corporation (BBC) to reject Argentine versions of the fighting so far and broadcast the British view to Latin America. In reply, Argentina has begun jamming three of the four BBC transmitters aimed at Argentina itself. BBC engineers have begun work on ways around the interference.
The British government has been specifically concerned to deny Argentina's claims that at least two Harrier jump jets had been shot down and that the Port Stanley airfield had suffered no damage from British air raids May 1. The British Defense Ministry dismissed these claims as ''fabrications'' May 3. It said British correspondents on board the aircraft carrier Hermes had counted the Harriers leaving the ship and the same number returning. The reporters had also seen aerial photographs of the damage to the Port Stanley runway.
Similarly, Britain has been using Foreign Secretary Francis Pym's latest US visit to remind everyone, including Argentines, that: (1) Britain is counting on US logistical support, and (2) is keeping the door open to further mediation attempts, for instance, by United Nations Secretary-General Javier Perez de Cuellar.
The ''back to the wall'' comment came from a former flag officer of the British submarine force, Vice-Adm. Sir Ian McGeoch (ret.). He is said to be in close touch with former colleagues. And reflecting the general military air of confidence so far, he told interviewers flatly May 3 that Argentina had failed to think through the military implications of its seizure of the Falklands last April 2.
British confidence stems from both its series of air and naval successes so far and its lack of losses.
When Britain retook the island of South Georgia, it put out of action one of Argentina's four submarines, the Santa Fe, and took almost 200 prisoners. In the last few days, the British task force says it has cratered both Port Stanley and Goose Green airstrips on the Falklands, shot down a supersonic Mirage fighter and a subsonic Canberra bomber, damaged another Canberra, and seen Argentine ground fire damage one of Argentina's own Mirages.
Thereafter, according to the Ministry of Defense May 3, a British submarine hit the General Belgrano with torpedoes just outside of the 200-mile exclusion zone, but allowed its escorts to escape. The cruiser carried 1,000 men, five-inch and six-inch guns, and helicopters. It was not known at this writing whether it had sunk or how many crew had been injured.
About eight hours later, early May 3, British Lynx helicopters north of East Falkland Island came under machine-gun fire from a patrol-craft-type auxiliary vessel (later described as a ''tug'' by a British reporter on the Hermes) and promptly sank it with missile fire. Another auxiliary vessel opened antiaircraft fire and helicopters inflicted damage on it. British fliers dropped lifesaving equipment nearby.
British Prime Minister Margaret Thatcher could now order the task force to continue enforcing the exclusion zone--a task made easier by the promise of fuel and supplies from the United States Navy.
This would save British lives, which Mrs. Thatcher needs to do to retain support here at home, and could avoid the kind of heavy Argentine casualties that might damage British support in Europe and the US.
The disadvantage of a blockade is that it takes time, with winter weather growing worse.
When British reinforcements arrive (paratroopers, helicopters, and 20 more Harrier jump jets) in a few days' time, the prime minister could decide to strike at Argentine mainland airstrips or sink more Navy vessels.
Or she could order Marines to occupy small areas of the Falklands.
At the moment, Britain is said to have about 18 warships on station, including two aircraft carriers, two cruisers, 10 frigates and destroyers, one assault ship, and three nuclear submarines.
Another assault ship is on the way together with 20 or more civilian ships including the cruise liners Canberra and Uganda, several ambulance ships, and assorted freighters and cargo vessels, and now the Queen Elizabeth 2.
The Defense Ministry said the QE 2 was necessary because it had the size and capacity to keep troops fit on a long voyage and the speed to get them to the South Atlantic quickly. It was also clearly designed as a spectacular measure, as headline-catching pressure--ordered so quickly that the captain of the QE 2 himself learned of the Navy order at sea May 3 from a BBC reporter who telephoned to ask for his reaction.