The cold Antarctic pie - who will get the biggest slice?

Oil, weather, and penguins' rights all jostled each other at the Antarctic conference held in inaptly sweltering Bonn this month. None of the three rivals really ''won'' this time around, as was to be expected in a conference that is aiming at the far-off deadline of 1991.

But disgruntled ecologist outsiders to the closed sessions feared that oil would eventually win, at the expense of the other concerns. And the 14-nation conference insiders, on the contrary, feared that oil might not win, and that 1991 might pass without an agreement on ground rules for exploitation of the fifth-largest continent's presumed riches.

''In a highly complex, difficult matter,'' warned West German conference chairman Alois Mertes, friends of Antarctica must ''find the common denominator of their differing interests and legal standpoints.''

For West Germany, he added - in an opinion that was echoed even by claimant states such as Chile and Argentina - protection of the unique and fragile environment of the earth's last frontier must have the highest priority.

Outside the conference hall, Greenpeace picketers in penguin costumes expressed skepticism. ''Exploitation will come before conservation,'' they predicted, if the region isn't turned into a world park.

And farther away, those other outsiders, the developing nations, chimed in that uninhabited Antarctica must be ''the common heritage of mankind.''

The divergent views didn't come tangibly closer at this ''Second Session of the Special Consultative Conference on Mineral Resources of the Antarctic,'' as the meeting was officially titled. But the two working subcommittees on definitions and environment protection did make a start. ''Definitions'' involve distinguishing between basic research, prospecting, and exploitation - and preventing any advance prospecting under the pretext of research.

Optimists place their hopes for eventual consensus on the strong common incentive to maintain international cooperation in Antarctica as a rare model of East-West (as well as North-South) working together.

The original 30-year Antarctic treaty, which was agreed on in 1959 and came into effect in 1961, regulates scientific research and bars introduction of military weapons, nuclear-power plants, or radioactive waste into Antarctica. A second treaty from 1980 allocates world access to krill and other aquatic life in surrounding waters.

On this pattern, optimists believe that eight years should provide enough time to hammer out a compromise - especially since the basic prospecting has not yet been done on this icebound continent that is larger than Europe. No one yet knows for sure if the region's supposed mineral wealth - an estimated 45 billion barrels of oil, 115 billion cubic meters of gas, copper comparable to Andean seams, coal comparable to Siberian seams, uranium, titanium, chromium, and iron - will really materialize.

Pessimists, on the other hand, contend that economic competition for Antarctica's putative mineral treasure is a lot harder to reconcile than research and fish. And they wonder whether the various groups of nations can manage to find Dr. Mertes's ''common denominator'' in the eight years left.

The first interest group consists of those states with territorial claims on the continent: the neighboring countries of Australia, New Zealand, Argentina, Chile, and Britain (through the Falkland and South Georgian Islands), and the explorer countries of Norway and France. Of these, the only nation to promote its demand by a population claim of sorts has been Argentina, which flew a pregnant citizen to Antarctica to give birth there.

The second group consists of further signatories of the 1959 treaty who have proven their scientific interest in Antarctica by manning permanent research stations there: the US, the Soviet Union, Japan, South Africa, and Belgium. Also included are West Germany and Poland, which later became full consultative members.

Together, the 14 nations in these two categories make up the consultative states, the body that just met in the Bonn conference. Together, they support 70 research stations in Antartica's 5.1 million square miles, with some 3,000 scientists and technicians measuring primarily ice, weather, and water.

A third category consists of the 13 signatories of the 1959 treaty which have never established research stations on Antarctica. These observers include such countries as Uruguay and Romania.

The fourth category consists of developing nations that have had no say in Antarctica to date, but think the continent should be kept as a common trust for mankind. These third-world countries, with Malaysia as a leading spokesman, plan to bring their claims to the United Nations in September, and to press for establishment of Antarctica as international territory on the pattern of open seas. The developing nations' political clout is limited, however, especially since their most populous members, China and India, are not fully backing Malaysia's bid.