London — At the bottom of the world lie 5 million square miles of emptiness, blanketed by ice that in places is three miles thick. At sea, icebergs can measure several square miles across: Five years ago a single super-iceberg stretched 30 miles from end to end.
The vastness of Antarctica, almost one-tenth of the globe's surface and 11/2 times the size of the United States, is inhabited by a few hundred scientists from 14 countries and by penguins and fish and krill, a tiny shellfish high in protein content.
Now, however, the rest of the world is taking increasing interest in the emptiness. The pace of scientific and diplomatic probing is quickening.
A number of countries are jockeying for position to be able to lay claim to chunks of territory, should the opportunity arise. They have their eyes on the copper, iron, and other minerals thought to lie beneath the ice and on oil and gas that could be locked in Antarctica's offshore continental shelf.
Leaders of the third world are insisting that the potential riches are the property of mankind in general, rather than belonging to a small group of wealthier countries.
Since 1961 the region (defined as lying south of latitude 60 degrees) has been kept free of military, nuclear, territorial, or commercial rivalries by a treaty that can be reviewed by any of the 27 signatories, beginning in 1991.
''It is a common misconception that the treaty actually expires in 1991,'' said a Foreign Office official here, ''and that its antinuclear, antimilitary protection will be lost. That, however, is just not so. The treaty goes on indefinitely, though under Article XII, it can be reviewed.''
Among recent developments that are bringing Antarctica closer to the spotlight of world attention:
* The 14 states actively involved in Antarctic research met in Bonn July 11 to 22.
Their aim: to continue the complex process of trying to hammer out what diplomats call a ''minerals regime'' - an agreement on who can lay claim to what minerals, how those minerals might be explored and extracted, and how the fragile ecology of the area can be protected.
The Bonn sessions were the third in a series of mineral talks that began in June 1982 in Wellington, New Zealand. They will be continued. No early decisions are expected.
* A number of countries have expanded their research budgets to make the most of the years before 1991, in case a review conference does meet and conditions change.
Argentina and Chile have long laid claim to the territory Britain uses for research. Interest in just how rich Antarctic mineral deposits, including oil, might be is growing, with some countries speculating that early in the next century Antarctic oil could be as valuable as North Sea oil is today.
So Britain has virtually doubled its scientific research budget for 1983-84 and for the two following years, from (STR)5.7 million a year ($8.5 million) to about (STR)10 million.
British officials are still discussing how to spend the extra money, but they make it clear that most of it will go into more research on minerals and such marine life as krill.
They deny that the extra money was allocated because of the Falklands campaign last year, but freely concede that the Falkland Islands are a necessary staging post and jumping-off point for British work in the Antarctic.
Australia, New Zealand, the United States, and the Soviet Union are all reported to be spending more.
* The third world put Antarctica on the agenda of the recent nonaligned summit meeting in New Delhi. Malaysia has been among countries at the United Nations in New York urging that the rich nations of Europe and North America, together with the Soviet Union and Japan, should not be allowed to retain a ''monopoly'' on Antarctic resources.
In the background is the possibility Argentina or other powers might try to open up Antarctica for strategic military uses, such as reconnaissance flights or weapons testing.
''I don't see that, though,'' said an official of the British Defense Ministry. ''Antarctica is strategic in the sense that it possibly contains copper, iron, oil, gas, and so on.''
A senior Defense Ministry source commented: ''Antarctica is an issue of much interest, and we'll be focusing on it more as 1991 approaches.''
The nations meeting in Bonn included the seven that claim jurisdiction over areas of Antarctica (Britain, Argentina, Chile, Norway, Australia, New Zealand, and France). Their claims are not recognized by other countries.
Also in Bonn were the US and the USSR, which as yet have not laid any formal claims themselves, preferring to reserve their rights for the future. The other attendants were the five other ''consultative'' states with bases in Antarctica (Belgium, Japan, West Germany, South Africa, and Poland).
''When the original Antarctic treaty was ratified in 1961, all references to mineral resources were dropped,'' said the deputy director of the British Antarctic Survey, Dr. Raymond Adie, in an interview. ''Otherwise there'd have been no treaty at all.
''Now is the time to start looking at mineral resources and what to do about them. Since 1961 we've added to the treaty a convention on conserving seals, and another on living marine resources such as krill. The effort now is to try to sort out which countries have what sovereignty. Would the Australians, for instance, allow the Soviets to look for minerals on territory Canberra claims?''
So far there has been talk of setting up a commission to govern all mineral resources, aided by a scientific and technical advisory committee. Much survey work remains to be done. Commercial companies will not invest until they are sure of a stable legal and political framework.
But Dr. Adie emphasizes the importance of protecting the Antarctic environment.
''An oil spill,'' he said, ''could completely destroy marine fauna on the continental shelf. Oil doesn't degrade in cold weather the way it does in hotter climes to the north. On land, an iron mine would create dust, which could be blown across the ice belt and cause it to melt. Flora and fauna would be upset and destroyed. . . .''