Washington — If Britain seeks to expel Argentina from the Falkland Islands with a combination of air, sea, and ground forces, its mission is replete with problems and dangers, say defense experts.
But the daunting task of resupplying a force 8,000 miles away from home bases and storming onto heavily defended islands is not beyond its capacities, they stress.
If the British capture of frigid South Georgia signals an Anglo-Argentine war over the Falklands, as now seems possible, Britain faces the task of setting up an effective air blockade of the islands. It would also face the task of landing a sufficiently large and heavily armed force to neutralize between 8,000 and 10, 000 Argentine troops now dug into the Falklands.
According to The Times of London, an advance contingent of Royal Marine commandos has already landed in the Falklands, an assertion denied by the British Ministry of Defense.
''If the opposition is pretty strong and you don't have a very good, orchestrated, and powerful capability, you just don't get ashore,'' declares John M. Collins, senior specialist in national defense at the Library of Congress.
Combined operations are ''the most difficult kind,'' naval expert Norman Polmar adds, ''especially when the enemy is waiting for you at virtually the extremity of a very long logistics line.''
The problem of refueling and resupplying the British flotilla - which includes the aircraft carriers Invincible and Hermes and the assault ships Fearless and Intrepid - is a formidable one British naval officers admit, but not an insuperable one.
Collins is less sanguine. ''You're looking at a logistical nightmare,'' he says.
The only significant stepping stone Britain can use in its South Atlantic operations is Ascension Island, where the Union Jack has flown since 1815 and which lies some 3,500 miles from the Falklands. Reportedly troops and supplies continue to pour into the island by air.
But Collins is not impressed with the island's utility. ''It sure isn't a very good staging area or a resupply area,'' he says. ''It's like calling Diego Garcia a good staging post for operations in the Middle East when it's 2,000 miles from the Strait of Hormuz.''
Nevertheless, say defense analysts, Ascension Island is better than nothing. The Royal Air Force is already flying its Nimrod anti-submarine and ocean surveillance aircraft from the island in support of the naval task force, though the aircraft lack the range to operate over the Falklands themselves.
If Britain employs its Vulcan bombers (now carrying conventional instead of nuclear weapons) against such Argentine targets as military airfields and the naval base at Comodoro Rivadavia, they might sortie from Ascension.
The Ministry of Defense in London recently announced that the range of a number of Vulcans is being extended for possible action against Argentina. ''Anything like that will just cause the Argentines more concern, whether its being done or not,'' Mr. Polmar says.
The delta-winged Vulcans carry 21 bombs of 1,000 pounds each and can be refueled in the air.
Two other British islands in the South Atlantic - St. Helena and Tristan da Cunha to the south of Ascension Island - seemingly have nothing to offer in the present crisis. Neither has an airstrip.
''There are certainly no facilities there which would be of any advantage to the Royal Navy,'' says a British source who asked not to be identified. Reactivation of the defunct Simonstown Agreement by which the Royal Navy was permitted use of the Simonstown naval base near Cape Town is not likely according to the source. Britain canceled the agreement with South Africa in 1967.
With the recapture of South Georgia, some 800 miles east of the Falklands, Britain now has a safe haven in the midst of an inhospitable ocean, though the 90-mile long island lacks an airstrip and any real port facilities.
Essentially most of what the British fleet needs - from aviation fuel and spare parts to cocoa and frozen peas - has to be shipped some 8,000 miles from Britain. Some items, however, can be flown to Ascension Island and loaded aboard transports there.
''You must look at things in perspective,'' says a British source. ''The Royal Navy has for a long time operated a long way from home. Distances of 8,000 miles are not in themselves exceptional.'' But he concedes that it has rarely conducted operations so far from a forward operating base.
Appreciating this, the Admiralty in London has reportedly dispatched its war fleet with a train of support ships. In all, the Royal Navy can muster 14 tankers, 4 fleet replenishment ships, and 3 stores-carrying vessels.
''I think you can forget the supply lines,'' asserts Brookings Institution fellow Michael MccGwire. In his view, supply poses no inordinate problem as no shipment of ''massive equipment'' is involved. MccGwire, a Briton and an expert on the Royal Navy, believes there will not be any great expenditure of munitions onshore. And transporting fuel ''is just something we've always been good at,'' he says.
But the Admiralty may well be regretting that it transferred an air stores support ship to the US Navy in 1980. It may also regret that it scrapped the heavy repair ship Triumph earlier this year.
The Triumph could have attended to battle-damaged ships at Ascension Island. Without it, they will have to slog their way back to Gibraltar for repairs.Bad weather could also damage vessels in the flotilla. For the next six months, violent storms will lash the waters around the Falklands, restricting sea and air operations on both sides. In fact, the region's appalling winter weather, with other factors, make a good argument for speedy landing of British assault forces. Their combat-readiness cannot be improved by weeks at sea in cramped conditions, a prey to boredom, apprehension, and sea-sickness.But the Royal Navy is no stranger to storm and tempest. It sails too frequently in the North Atlantic for that. If anything, the Antarctic-like temperatures to be found in the South Atlantic are a greater threat than the weather, affecting the performance of ships and crews. But supplies and storms aside, can the Royal Navy send Argentine warships to the bottom if the need arises? ''My presumption is that what the Royal Navy puts down there from a naval battle standpoint is going to be pretty hard to compete with,'' says John Collins. A British naval officer adds: ''I would have thought it was very adequate.''Michael MccGwire is convinced that Britain's nuclear-powered hunter-killer submarines will have no trouble disposing of Argentina's surface fleet, a view shared by US experts. As many as five may now be prowling the Falklands. Extremely quiet submarines, carrying anti-ship missiles besides their torpedoes, they make seaborne resupply of the Argentine forces on the Falklands a perilous undertaking, though they would wish for deeper water. A prime target for the British submarines will undoubtedly be the aging Argentine aircraft-carrier 25 de Mayo, (launched in Britain in 1943 as HMS Venerable, with its 14 US-made Skyhawk attack aircraft).MccGwire believes it is ''conceivable'' that an Argentine submarine could slip in amongst the British fleet, but says the possibility ''is not very likely.'' The Royal Navy is particularly adept at antisubmarine warfare, experts say, noting that the Argentine Navy now only has three submarines at its disposal. According to one report, the Argentine Navy has been reduced to only two usable submarines (although, according to earlier reports, Argentina would still three subs left after the attack on the sub at South Georgia). The Santa Fe, which began life as the US submarine Catfish in 1944, was badly damaged during the British attack on South Georgia. The Buenos Aires newspaper La Prensa has since reported that it was scuttled by its crew to prevent its falling into British hands.Argentina's slender submarine force would, of course, also be liable to destruction by the Royal Navy's hunter-killer submarines. In the key area of electronic warfare, the Royal Navy is acknowledged to have a considerable edge over its Argentine counterpart. It should be able to jam communications between the Falklands and Argentina and within the islands themselves, something that could play havoc with the junta's attempts to coordinate defense of the islands they seized April 2.Britain may even be able to read Argentina's naval code, which would assist it in deploying its forces. ''I'm certain the US can,'' says Polmar, ''and we are probably closer to the Brits than any other nation as far as intelligence cooperation.''Both combatants are reportedly getting spy satellite information on each other's fleet movements from their respective superpower friends. In their attempt to relieve the Falklands, British defense chiefs are thought to be chiefly concerned about the air power Argentina can deploy and the size of the Argentine force occupying the islands. Reportedly tanks, artillery, and minefields could greet assaulting British forces.''The airpower for an amphibious landing is pretty limited,'' John Collins declares. Even if the airstrip at Port Stanley can be lengthened in time (there are some reports it has been lengthened), it is unlikely that Argentine aircraft will be permitted to use it at Port Stanley in any battle. A first priority of British forces will be its destruction, say defense analysts - as much to prevent further air resupply of the islands as any use by fighter aircraft.The Argentine Air Force has the advantage of southerly land bases, which enable it to conduct regular sweeps over the Falklands. But the Argentine Skyhawks are slower than the British Harriers and lacks radar. Moreover the British machine, a vertical take-off jet, needs no airstrip to operate from and could be deployed at many spots on the two islands. In addition, attacking Argentine aircraft will have to contend with the anti-aircraft defenses of the British fleet.Although the British flotilla has lost strategic surprise it retains the important element of tactical surprise and can presumably land its Royal Marine commandos wherever it chooses on East or West Falkland Island. Even if Argentina had 20,000 men on the islands they could not guard 800 miles of rugged inlets and bays say analysts. ''They don't know from which direction we're going to come,'' says MccGwire. But military planning has a way of going wrong and nobody in the Royal Navy flotilla has forgotten that the Argentine Navy possesses two modern, British-built destroyers, the Hercules and Santisima Trinidad.Some analysts here believe that - buoyed by its success on South Georgia and conscious of the enormous cost of the operation and the danger of keeping troops on ships too long - Britain may decide to launch a major landing on the Falkland Islands in the next few days.