"The world's first satellite war" is how Arthur C. Clarke, science-fiction writer and originator of the communications satellite concept, recently described the fighting in the Persian Gulf.

In addition to spy satellites that scour Iraq for military targets, U.S. troops are also relying on dozens of other spacecraft that can guide them across featureless deserts, warn of bad weather, relay communications, update maps and watch over such potentially strategic resources in Iraq as water and farm harvests.

"You've never had a war that's had this much space support," said John Pike of the Federation of American Scientists. Formerly, "satellites were for generals. Now it's the lieutenants and captains that are using them."

In a few cases, the Iraqis may be, too. Some experts believe they are poaching pictures that are electronically transmitted from space by other countries' weather satellites. These could be used to predict movements of clouds and keep their mobile Scud missile launchers hidden beneath them.

For communications, the Pentagon is relying on both commercial satellites and its own. The most important traffic is going over the Defense Department's private satellites, notably two major systems parked in orbits 22,000 miles up. Satellites run by Britain and the North Atlantic Treaty Organization are also believed to be in use.

These satellites transmit messages ranging from telephone calls to computer files, helping the armed forces deal with everything from personnel records to munitions inventories. Portable satellite dishes erected in the Saudi desert have extended the Pentagon's in-house communications systems to countless buildings and tents there, channeling telephone calls, facsimiles and data in huge quantities.

Satellite antennas are standard equipment on warships' superstructures and on some warplanes. On the ground, portable earth stations painted in camouflage can be trucked into battlefields and set up in minutes.

These easy communications can keep down the size of the U.S. presence and provide minute-by-minute reports of action in the field, experts note. But as Paul Manson, former chief of the Canadian Defense Staff, remarked, satellites can also mean that far-away generals "micro-manage elements of the battle that they shouldn't be touching."

The Pentagon also uses weather satellites to plan air strikes or locate clear skies where jets can meet refueling tankers. Commanders on the ground can get weather data directly by pointing small dishes into space.

Government-related companies that sell "remote sensing" images from space -- EOSAT of the United States and Spot Image of France -- have been selling their services to allied forces to update military maps and survey things like how many acres of farmland Iraq has under cultivation. The size of Iraq's harvests this fall, for instance, might give clues to its food supplies and ability to withstand an extended war.

Spot, which has more powerful cameras than EOSAT, has suspended sales of gulf images to anyone but allied governments, on the grounds that they might reveal to Iraq tactical intelligence about allied troop positions. EOSAT has kept up its open sales, arguing that it is legally bound to do so.

Of all the satellites in use, the Navstar Global Positioning System is the least-tested in military operations. The system's role is to save allied soldiers from an age-old problem troops face in war: getting lost.

Each satellite in the system emits beacon signals, which are received by special black boxes carried by many allied vehicles, airplanes and infantry units in the gulf. From these signals, each box calculates its own geographic coordinates, with a claimed accuracy of 50 feet. For troops moving across the featureless Saudi desert, this can be the only means of finding their way.

In addition to navigation, GPS has strictly military applications. B-52 bombers use it to time the release of their bombs from high altitude. Artillery commanders can draw on it to aim their guns.

GPS can also be used to mark a path through a minefield. Instead of marking a field with flags that the enemy could also see, troops would give friendly units the GPS coordinates of the safe corridor.

The Iraqis are believed to have a few GPS units (GPS is widely used in the oil exploration industry), but have not integrated their use into their military the way the allies have.

At a cost of $10 billion, the Pentagon envisions a system of 21 GPS satellites by the mid-1990s that could be used by soldiers and civilians around the world. For now, the system does not provide full, 24-hour-a-day coverage because there are only 16 satellites in orbit.