While U.S.-Soviet relations seem to be slipping back into the Cold War era, there is one place in the world where the two rivals have put their hostility into a deep freeze: Antarctica.

This peaceful coexistence was based on a treaty signed by the two superpowers and 10 other nations in 1959 to set aside Antarctica exclusively for non-military scientific research. Antarctica has not been regarded as a vital interest for either the United States or the Soviet Union, so the treaty provisions have been adhered to scrupulously. American scientists are allowed to work at Soviet bases; Russian scientists are welcomed at U.S. bases.

Lately, though, the CIA has intruded into this icy idyll. The discovery of oil, other minerals and enormous schools of tiny, high-protein shrimps called krill have made Antarctica suddenly worth CIA scrutiny.

What has stirred the CIA's interest most is the Kremlin's increased interest in Antarctica. Anytime the Russians decide an area is worth greater attention, the CIA gets nervous. Now, apparently, they are worried about a Frostbite Gap at the South Pole.

The CIA has used satellite spies and communications equipment to monitor Soviet activities in Antarctica, and has gleaned much useful information about Russian expeditions.

A "Top Secret Umbra" document reviewed by my associate Dale Van Atta shows the extent of the CIA's interest in Soviet operations in Antarctica.

Seven permanent Russian bases are established there -- compared with four permanent American installations. An eighth, part-time Soviet base, Druzhnaya, is in operation only during the Antarctic summer, which lasts from November to March. Construction of that base touched off the first disagreement over the multinational treaty.

The Soviet announcement that the Druzhnaya base "would be used for geological and mineral exploration was interpreted by some as a breach of the agreement," the CIA report states. But it adds that Soviet officials were "quick to stress" that the exploration would be "scientific rather than commercial in intent." What has the scientific community concerned is that commercial drilling could lead to oil spills, which might destroy the beds of krill that are the foundation of the continent's delicate ecology.

The CIA added that the Soviets' meteorological research is "facilitated by the use of small sounding rockets launched from the Moldezhnaya station." But this does not constitute a breach of the 1959 agreement, which forbids only military rockets.

"Probably the most significant measure of the growing Soviet interest is the number of scientists on each expedition who stay through the austral winter," the CIA explains. By the CIA's tally, about 250 Russian scientists made the unenviable winter stay for the 1976-77 season, compared with only 100 hardy Americans. On the other hand, during the Antarctic summer, the American complement jumped to 900, while the Russian personnel numbered only about 600. The CIA also noted that while the American contingent is supplied with helicopters and C130 transport planes, the Soviets stick pretty much to sea transportation.

But the CIA wonders why the Soviets have increased their spy-satellite activity over Antarctica, and have been using more sophisticated satellites over the South Pole. As CIA sources explain, satellites are expensive, and both the Russian and the Americans use their limited number of satellites to cover only areas of intense interest.