WHEN talking about arms control, former President Ronald Reagan used to say, "Trust, but verify." This verification takes place at Pine Gap, a military base shared by the United States and Australian governments, about 20 miles out of Alice Springs.Pine Gap, named for a mountain pass in the Macdonnell Ranges, holds one of the largest ground-satellite stations in the world. Pine Gap technicians can maneuver satellites over the Soviet Union, or the Middle East, to collect intelligence data on missile launches. In the new era of nuclear disarmament, verification and Pine Gap have taken on new importance. Any new arms deal, such as President Bush's recent offer to eliminate mobile intercontinental ballistic missiles, will include Pine Gap's participation. So when other military bases are shrinking, Pine Gap appears to be expanding. Australian Prime Minister Bob Hawke told Parliament in 1988 he would boost the Australian proportion of the 500-member staff from 10 percent to 30 percent by 1991. "We understand they've got three new antenna systems," says Russell Goldflam, a member of the Alice Springs Peace Group. Neither the Australian Department of Defense nor the US Information Service in Canberra would comment on the base. Pine Gap was instrumental during the Gulf war; it was able to alert Patriot missile commanders in Saudi Arabia and Israel about Scud launches in Iraq.Pine Gap also collects other intelligence data, including film for the Central Intelligence Agency, the US agency responsible for the base. At least twice a week, film is transported by the US Air Force to a base near CIA headquarters in Langley, Virginia. This operation concerns Mr. Goldflam most: "If Pine Gap is used for electronic warfare, we find that unacceptable." Goldflam believes Pine Gap is also involved in the development of the Strategic Defense Initiative. "This is just not in the best interest of Australia," he argues. Recently Mr. Bush offered to discuss the sharing of early-warning information with the Soviets. Bush said he would be willing to discuss "confidence-building measures, like mutual visits to early warning facilities and possible officer exchanges at those facilities." The possibility of Soviets marching into south Australia generated the headline: "US to let Soviets in on our secrets." Mr. Hawke and Sen. Gareth Evans promptly denied the imminent arrival of the Soviets and said Australia would be part of any discussions about information sharing.