The new military spy satellite carried into space on Friday is viewed by some experts as capable of gathering such important information that it is only a matter of time before the Russians begin to think of ways to destroy it in the event of war.

Like the roughly 200 military satellites already deployed in space by the United States and Soviet Union, the $500 million Lacrosse satellite reported to be aboard the space shuttle Atlantis is not armed. It is a surveillance satellite, carrying a sophisticated radar that can look down from space, piercing even cloud cover to reveal what's happening on the ground."As military satellites become more directly applicable to actual combat, they become much more attractive targets for destruction," said John Pike, an expert on space systems with the Federation of American Scientists here.

"Lacrosse provides a good example of that," he said. "It's going up there to find targets for the new Stealth bomber and to look for long-range targets deep behind the lines in the Warsaw Pact. Now, if I've got all that riding on my satellites, the Soviets would be crazy not to try to shoot them down."

"Space is already militarized," agreed William Arkin, an authority on nuclear weaponry with the Institute for Policy Studies, a liberal think tank in Washington. "The question is whether we're going to avoid the weaponization of space."

The United States now has approximately 75 to 80 military satellites in space, while roughly 125 of the 150-plus Russian satellites now in orbit are thought to have some military use. The numbers are approximate, because neither government talks about the matter.

The Pentagon, for example, considers the Atlantis launch a classified military mission for which no information will be provided. It will neither confirm nor deny that the cargo is a radar-imaging satellite.

As approximate as the tallies are, they demonstrate the growing reliance of the two superpowers on military space systems. It was only three decades ago - in 1957 with Russia's Sputnik - that mankind developed the ability to put a manmade object into orbit.

Now, military satellites are in orbit spying on facilities and forces, scanning the radio waves as electronic ferrets, watching for nuclear explosions or missile launches and mapping the Earth's surface.

Even the seemingly mundane tasks in space have become important for war-fighting. Communications is an obvious example, but there are others.

For example, the latest generation of navigation satellites helps provide the pinpoint accuracy now claimed for nuclear missiles like the giant MX. Among other functions, these satellites allow the military to synchronize its watches down to billionths of a second.

And scrutinizing the weather becomes essential in the event of a war. Both the United States and Soviet Union are operating advanced meteorological satellites to aid low-level bombers, detect solar flares and find holes in cloud cover for reconnaissance work.

The United States now has 20 military satellites of various types waiting to go into orbit - victims of the launch hiatus forced by the Challenger disaster and unrelated problems with unmanned Titan boosters.

As that backlog is slowly erased, Arkin, Pike and others suggest the Pentagon - and perhaps the Kremlin - will face other problems with their satellite hardware besides protecting them as tempting targets.

"The expense of these new types of satellites is not to be believed," says Arkin.

"We're going to have to look at a single satellite the way we look at an aircraft carrier. These satellites alone are costing $250 million and up."

Such complaints don't bother Pentagon officials, because they see no alternative.