It is simple enough to write the standard scenario for the recapture of the Falkland Islands.

Great ships of the line lay off shore bombarding Argentine positions. Landing craft and amphibious tractors form up at a line of departure and head off in waves for the beach. British fighter-bombers strafe and fire rockets at the shoreline until the instant the Royal Marines storm ashore. Within a few days the Union Jack flies again over the port of Stanley. There are many white crosses but a great victory has been won.

This, of course, is an old scenario for island fighting in the Pacific in World War II, and it is just as dated.

"The era for that kind of amphibious assault," a U.S. Marine colonel insists, "is entirely over. The naval gunfire it requires no longer exists, not even in the U.S. Navy."

The British fleet now steaming south toward the Falklands is poorly equipped to provide covering fire for a landing, according to reports from London. It includes five destroyers and nine frigates, a small force by World War II standards.

There are other serious hazards to a frontal assault on the island. In virtually every Pacific landing in World War II, the American Navy had total air superiority. That is not the case here.

The British are bringing two aircraft carriers with 40 vertical-takeoff Harrier warplanes and 40 to 50 helicopters, which could provide limited air support for a landing.

Argentina has about 250 combat aircraft, including 113 fighters and interceptors and 23 helicopter gunships, U.S. sources say.

Britain would operate at a disadvantage in the air against this force, partly because the Harriers have a range of only 100 miles when fully loaded, military sources say. The Argentines can reach the Falklands from at least five major mainland air bases.

Another problem facing the British is the ground-force ratio. The rule of thumb in World War II island fighting was that the invading force required a manpower advantage of three or four to one, but British invaders would most likely be outnumbered in the Falklands.

The British force of Marines and commandos is reported to number no more than 5,000 or 6,000. Argentina has put 7,500 to 10,000 troops on the island with food for 60 days and ammunition for 20 days of combat. C130 transports bring in new stocks daily, press reports say.

Argentine troops on the island are equipped with standard infantry weapons--Belgium model FAL automatic rifles, 80-mm and 120-mm mortars, 105-mm howitzers and recoilless rifles, and armored landing vehicles on which 20-mm guns or 50-caliber machine guns can be mounted.

Tanks are unsuited for the terrain. A British journalist who visited the island more than a year ago wrote: "It is inhospitable country, peat bog and fell, dotted with place names which suggest its bleakness: Tumble Down Mountain, Mount Misery, Bluff Cove, No Man's Land. Crossing 20 miles of it by Land Rover will take six hours on a good day. The peat collapses, wheels go up to their axles in mud and bog water, jacks and planks are produced, passengers are instructed to heave. It happens every mile or so."

Argentine antiaircraft batteries have been spotted in recent days around the airstrip at Port Stanley where interceptors reportedly are based. The strip is not an ideal operational field. When the Army chief of staff, Maj. Gen. Jose Vaquero, landed on the island in a Fokker 28 earlier this week, the fierce cross winds flipped the plane on its back, according to an American official.

The winds reach 80 knots at times during this season of the year, creating 30- to 40-foot seas, another impediment to an amphibious assault.

There are two imponderables about the Argentine island defenses. The level of fortification is one of them. The Pacific landings of World War II were made terribly costly by the strength and ingenuity of the Japanese defenses--intricate cave and tunnel systems, bunkers and pillboxes of steel and concrete, and artillery and mortar batteries aimed at potential landing beaches. There is no evidence the Argentines have attempted anything so ambitious.

The other imponderable is the staying power of the Argentine troops. They are led by professional officers and noncommissioned officers, but the ordinary soldier is a draftee serving only eight to 14 months. The educational level of the draftees is said by Argentine officers to be very low.

"The real preoccupation of the Army," one officer said, "is with internal subversion. We don't think much in terms of conventional war. We have no history of warfare whereas the British history is impressive."