When the U.S. space shuttle launches a secret Air Force satellite next month, it will mark only the latest phase of an ongoing 25-year contest in which the United States and the Soviet Union use highly technical space satellites to keep track of each other.

James M. Beggs, head of the National Aeronautics and Space Administration, which will rocket the shuttle carrying the military payload into space from Cape Kennedy, said last night that he sees the launch as a business proposition, not a sudden militarization of America's space program for clandestine purposes.

To NASA, Beggs said, the Air Force is another customer for the nation's space truck, the shuttle, whose rental fees will reduce the cost of the program and free money for civilian space exploration. He said secrecy on the launch "is a matter of customer preference."

The business of overhead surveillance through the years has become an integral part of the relationship between the two superpowers. One reason that military satellites have been used so extensively by both sides is that they are less provocative than highly visible and intrusive manned systems such as planes and ships.

The Library of Congress has compiled figures showing that over half of everything the United States and Soviet Union send into space has military application, including photographing, listening, communicating, navigating, targeting, warning, searching and weather forecasting.

The U.S. military efforts in space have been marked by wide swings in the amount of information made public. At one time the government handed out press kits that supplied many details about U.S. satellite capabilities. Most recently, the Pentagon has strongly discouraged any speculation about the upcoming space shot.

More than 15 years ago, in this on-again-off-again government secrecy the once supersecret photographic spy satellite called Samos was displayed in the Smithsonian Museum. The U.S. government apparently wanted to assure the public that it could keep track of the Soviets, an assurance that Congress demanded before approving the arms control treaty known as SALT I. Samos did not stay on display long, the victim of another swing in government policy.

The grand-daddy of the U.S. overhead surveillance program was the U2 spy plane built for the CIA in the Lockheed Corp. secret "Skunk Works" in Califorina. The U2's wings were built so long and willowly for high altitude flight that they had wheels on the end so they would not drag along the runway on takeoff.

The U2 flew over the Soviet Union repeatedly in the 1950s, its cameras taking pictures of military installations as well as MiG interceptors which could not reach the altitude of the U2. When the U2, piloted by Gary Powers, was shot down by the Soviet Union on May 1, 1960, it forced a re-evaluation of the national effort to gather information about the Soviet Union. Both superpowers turned to satellites to monitor each other from space.

Neither superpower protests this spying by the other. There is something akin to an acknowledgement of parity here, if no place else in the rival arsenals.

Under the Outer Space Treaty of 1967, the United States and Soviet Union even go so far as to disclose to each other through the United Nations when they have launched a satellite into space as well as its flight path. The mission and capabilities of these space vehicles are not disclosed, however.

The ever-advancing technology that enabled the United States, and later the Soviet Union, to load several bombs on one rocket and send each warhead to a different target -- or MIRV for multiple, independently targetable re-entry vehicle -- has also transformed spy satellites. One satellite can do a number of things from its perch in space, such as take photographs and transmit them to earth and record radio talk and telemetry. The old Samos was crude by comparison. It would eject a packet of film as it flew over the Pacific Ocean and an Air Force plane would snatch the film package out of the sky with a hook.

The Library of Congress 1984 report on international space activities dramatizes how cramming several military functions into one long-lived satellite has lessened the need for repeated launches. In 1962, two years after the downing of the U2, the Defense Department conducted 31 successful space launches. By 1983, thanks largely to long-life, multiple-mission satellites, the military launch figure had dropped to seven. In 1962, according to the study, the Soviets conducted their first five military space launches. The number went up to 58 for 1983.

Since one rocket, or space shuttle, can put many payloads into space, the more meaningful measure of U.S.-Soviet military space activity is military payloads. Here the Library of Congress study estimates that for 1957 through 1982, the United States put 455 military payloads into space and the Soviets 1,252.

Both superpowers put a high premium on getting pictures of the other's missile bases and other military installations. The United States in the 25-year period put 236 low-flying photographic satellites into orbit and the Soviet Union 558, according to the study. Collecting electronic intelligence with so-called ELINT satellites was also of prime interest to both countries, as evidenced by the U.S. putting 81 ELINTs in space and the Soviets 74 in the 1957-82 period covered by the study.

The satellite the Air Force plans to launch from the shuttle next month is believed to be a more sophisticated version of the older Rhyolite satellites whose electronic intelligence-gathering mission was compromised by a TRW Inc. employe who spied for the Soviets.