London — For Britain, the cost of occupying the distant Falkland Islands in the next three years is just over $5 million per island family. The latest figures from the Ministry of Defense put the total sum for the three years at (STR)1,860 million, or $2,622.6 million.
About 500 families live on the bleak, windy, sheep-raising islands. They are 8,000 miles from Britain and 600 miles from the Argentine mainland.
Two years after Britain went to war to force Argentine troops off the islands , such large bills remain controversial here.
Critics argue that the costs, including the expenses of a garrison of about 4 ,000 troops, are far too high for Britain's ailing economy. Nor is any end in sight, since a final diplomatic solution to the islands' status remains blocked.
Prime Minister Margaret Thatcher replies that principle is at stake: The 500 families there wish to remain British. London has an obligation to them - and to its soldiers who were killed in the campaign.
Now Defense Ministry officials are making new efforts to counter the criticisms on other grounds.
In a meeting with a group of overseas correspondents, John Stanley, the minister of state for the armed forces, said the bills for the garrison were actually less than they appeared to be.
''Half of the total amount is the cost of replacing ships, equipment, and so on lost in the war,'' he said. ''Those replacements are defense assets, which can be used anywhere in the world. . . .
''The figures also include about (STR)200 million ($280 million) for the new airport at Mount Pleasant (which has a lengthened runway able to take long-range cargo and military aircraft).
''When that airport is completed, the cost of the garrison on the islands will fall.''
One factor he cited was that the cost of refueling Hercules transport planes in the air on their long runs to and from Ascension Island in the South Atlantic would end. The Hercules have to be refueled by aerial tankers twice on each leg.
''The hump in our Falklands costs comes in the next two to three years,'' Mr. Stanley went on. ''After that, the costs will be a very small proportion of our overall defense budget each year.''
Britain's defense budget for 1983-84 is (STR)15,973 million ($22.3 billion). This includes (STR)624 million, or 3.9 percent, for the Falklands.
The opposition Labour Party has criticized the government for inept planning and management in providing new housing on the islands.
While opposition parties share Mrs. Thatcher's desire to protect the rights of the Falklanders themselves, they would like to see more flexibility in the British negotiating position.
But the prime minister is adamant that her government will not discuss any change in British sovereignty over the islands.
The new Argentine President, Raoul Alfonsin, is reportedly maneuvering to find a way to start ''conversations'' that could ultimately lead to talks on topics including sovereignty.