The high-tech ears and eyes of U.S. intelligence are fighting their first large-scale hot war in much the same way as they have waged decades of cold war -- cloaked in secrecy and, by all accounts, with growing effectiveness.

But the death of numerous civilians in Baghdad last week when U.S. bombers hit a building identified by American intelligence as a military bunker -- and said by Iraq to be a civilian shelter -- has put new pressure on authorities here to reveal more about the space-age means used to collect information on such targets.

Imaging satellites reportedly saw vehicles belonging to Iraqi military and civilian leaders arriving and departing, and listening satellites intercepted orders from inside the facility being radioed to Iraqi troops in Kuwait. At the same time, the spy network apparently failed to detect the sheltering of civilians in the building.

U.S. officials have declined to reveal raw satellite data that might prove their claim that the facility was a legitimate military target. Disclosing U.S. intelligence capabilities, they say, would enable adversaries to take effective countermeasures.

The complex spy system, with its almost-instantaneous global communications, includes the largest network of watching and listening satellites ever assembled in orbit, as well as manned and robotic reconnaissance aircraft, ground-based listening posts and human sources.

Military leaders have relied on the system to assess damage done by the air war in order to decide the best time to launch a ground assault. But according to independent experts, there are noteworthy gaps, given the field commanders' need for virtually minute-to-minute information.

"There's a lot of hype about the capabilities of these systems," said military analyst Paul Stares of the Brookings Institution. "People forget there's a lot of uncertainty in the intelligence business, despite some published reports on the 'all-seeing, all-knowing spy satellites.' "

The overhead spies include photo-reconnaissance satellites, an advanced radar satellite, at least two eavesdropping satellites with giant antennas, and a system of early warning satellites that give Patriot anti-missile crews a minute or more advance warning of Iraqi Scud attacks against Saudi Arabia and Israel.

The pride of the orbital fleet is said to be a group of perhaps half a dozen photo-reconnaissance satellites code-named Keyhole, each costing $1 billion or more. Each is like a Hubble Space Telescope but pointed down instead of up. In addition to collecting images in visible light, the more advanced Keyhole models use infrared instruments to detect variations in heat in darkness. They can distinguish objects as small as a human head from up to 500 miles away, analysts say.

Under certain conditions, these satellites should be able to tell whether people on the ground are wearing khaki uniforms or vari-colored civilian garb, but they would not see epaulettes or other signs of rank, according to John Pike, a military space analyst with the Federation of American Scientists.

On the other hand, even the Keyholes' eagle eyes may be too weak to estimate damage done to Iraqi trucks by allied cluster bombing. "A truck could be like swiss cheese, and you wouldn't see it in the images," Pike said. "Pieces of shrapnel the size of marbles could totally disable the truck."

One of the Keyhole satellites passes over the gulf region every few hours, analysts said, and the data can be forwarded to commanders in the field virtually instantaneously, though more typically it reaches them within days.

There are intervals of several hours at a time, when no imaging satellite is watching the gulf. And even when they are, clouds, darkness or the smoke of oil fires sometimes block their vision.

Analysts say the observing process may be further slowed when the amount of satellite data overwhelms photo-interpreters, highly skilled professionals who translate blurs and patterns into useable information. Some of them are based at the National Photographic Interpretation Center at the Washington Navy Yard.

In the case of the bombing Wednesday of the building in Baghdad, the most recent imagery had been taken at least 24 hours before the attack, according to the Pentagon.

"You have a tremendous amount of imagery coming down," said Jeffrey Richelson, author of "America's Secret Eyes in Space." "The amount and number of targets is certainly an impediment, not to mention the weather."

Another type of imaging satellite, known as Lacrosse, uses advanced radar and, unlike the Keyholes, can see through clouds, darkness or sandstorms. However, analysts say it lacks the Keyholes' ability to see fine detail.

Its radar eyes may, depending on the smoothness of the surface, penetrate some 15 or 20 feet below the desert floor to detect buried installations, according to John Ford of the radar sciences group at the Jet Propulsion Laboratory in Pasadena, Calif.

Tanks, guns and airplanes, unless hidden beneath radar-proof cover, "stand out like beacons in radar images," Ford said. But "radar won't tell you whether you've destroyed a tank . . . . A tank will look pretty much the same whether it's upside down or right side up."

Another disadvantage of the Lacrosse is that there is only one, according to military analysts, which means it sweeps the gulf only about once a day.

In what analysts describe as "the blackest of the black" programs -- meaning most secretive -- allied commanders rely on at least two eavesdropping satellites code-named Magnum and Vortex in stationary orbits about 22,000 miles above the Earth, as well as ground-based listening posts, to keep track of Iraqi radio and telephone communications in the VHF, UHF and microwave broadcast bands.

Because the Iraqis use Soviet-style tactics, allied electronics warfare experts are said to have considerable insight on how their communications reveal their order of battle. The Iraqis use evasive tactics, such as changing frequencies, and the allies try to track them using automatic frequency scanners, analysts said. The Iraqis might attempt to hide a military bunker by placing its large communications antennas half mile or so away, and by using buried cables -- whose transmissions cannot be snatched out of the air electronically -- to connect the center with the antennas.

Another type of satellite -- Air Force Space Defense Support Program craft -- recently has been positioned over the Indian Ocean to alert Patriot anti-missile crews and populations in Israel and Saudi Arabia when Scud missiles lift off from Iraq.

Some intelligence is also provided by the RF-4C Phantom reconnaissance plane, with cameras in its fuselage and limited weapons defenses. They are sometimes aided by "remotely piloted vehicles," which have limited flying range.