The relatively small number of U.S. warplanes lost during the initial phase of Operation Desert Storm apparently was due in large part to successful allied attacks on Iraq's ground control intercept (GCI) system, leaving Iraqi fighter pilots separated from their ground controllers, military officials said yesterday.

The Air Force had estimated the United States would lose between 25 and 40 aircraft in the first attack on Baghdad and other targets in Iraq in the pre-daylight hours of Jan. 17, officials said. But only one plane, a Navy F/A-18 Hornet, was lost.

Gen. H. Norman Schwarzkopf, commander of U.S. and allied forces in the Persian Gulf, said yesterday on NBC's "Meet the Press" that "we have almost completely taken out their ground control radars. As a result, their aircraft have been kept on the ground and kept very much in shelters."

Schwarzkopf added that U.S. bombers are continually hitting those shelters but said it is not known "how much damage we've done to date." He said Iraqi President Saddam Hussein "may be trying to husband those very valuable resources to use at some later time."

Since the initial allied attacks, however, Iraq has been feverishly repairing GCI centers and replacing damaged radars that are used to search for and shoot at enemy planes. This has impelled Air Force and Navy commanders to order fresh attacks on those targets in what has become a constant cat-and-mouse game between the attackers and defenders. U.S. pilots said their air battles have become increasingly tough since the first night.

Iraqi pilots are highly dependent on controllers -- who sit in front of radar consoles on the ground -- to tell them through radio commands what course to fly to intercept invading aircraft, officials said. The Iraqi pilots who did get into the sky despite the heavy bombing of air fields during the initial attack found themselves without this guidance, officials said.

"They were just up there flying around in random motion," said one military official briefed on the first night's raid. "They have a very centralized air system and we severed it," he said. There were 30 Iraqi planes that could have done battle, officials said, but they fled out of the Americans' path after a couple of them were shot down. No one in the GCI centers was in radio communication to issue attack instructions, these officials added.

Iraqi pilots did not have the equivalent of U.S. airborne warning and control system (AWACS) planes to fall back on for guidance. And they apparently did not want to rely on the radar in their own planes to fight U.S. air crews who have superior radar systems and are highly skilled at operating them, officials said.

The Iraqis could have organized an air defense even without GCI, said one Pentagon planner. "They have first-rate equipment and fourth-rate leadership," he said, noting that no Iraqi squadron commander in the sky attempted to direct his aircraft.

The retreat of the Iraqi fighter planes and the bombing of Iraqi air fields left ground-based anti-aircraft missiles and guns as the main threat to the U.S. aircraft. The missiles and guns are guided by a radar, called "fire control," that is different than the GCI radar. The fire control radar are spread out in numerous locations to defend key targets.

The location and characteristics of these fire control radars were pinpointed over the past several months, and their signals recorded, officials said.

Knowing the location of the anti-aircraft radar sites was crucial to destroying some of them with missiles that ride down the radar beams and blow up, experts said. Determining their frequencies and pulse widths enabled U.S. air crews to send the same signals back into the transmitting antennas, causing a confusing snowstorm of dots on the consoles being studied by Iraqi gunners on the ground. This kept most of them from shooting straight, officials said.

Radar-killing planes that flew on the first raid were armed with HARM and Shrike anti-radar missiles. Early versions of these missiles used against North Vietnamese gunners frequently were foiled by such simple tricks as blinking the ground radars on and off, causing the missiles "to go stupid," electronic warfare specialists said. Today's anti-radar missiles being used against Iraq are so smart that the targeted radar only has to emit for a few seconds for the missiles to find and destroy them, specialists said.

Trial by fire during the Vietnam War also led to the improvement of earth penetrating iron bombs, which are now being used against Iraqi troops in heavily fortified bunkers and command posts in Iraq and Kuwait. Some of these bombs are designed to dig themselves more than 10 feet into the sand before exploding, military sources said.

They added that the modern arsenal of earth-penetrating bombs being used against Iraqi strongholds in the desert include an an update of the Mark 36 Destructor, dropped by the thousands on Vietnam. Bombardiers call the Destructors "seeds" because they are sown in the earth but do not explode until a person, vehicle or ship goes near enough to them to activate the fuze by magnetic detection or vibration.

A Navy flier who helped develop the Mark 36 recalled yesterday that one of the Navy frogmen testing early versions of the bomb kept setting off the detonator, until it was discovered that the metal in the eyelets of his rubber shoes was enough to activate the sensitive fuze. Modern versions of that Mark 36 fuze can be attached to 500-pound, 1,000-pound or 2,000-pound bombs.

Part of the current bombing campaign against Iraq's Republican Guard units in Kuwait and southern Iraq consists of a one-two punch with bombs, military sources said. One type of bomb tears apart the bunker or command post and another burrows itself into the ruins. The latter bomb explodes if anybody or anything comes near its resting place, discouraging efforts to rebuild a bombed bunker or command post.

It is too early to say, sources said, whether such bombing will demoralize the dug-in Iraqi troops to the point they will give up rather than fight. But air power enthusiasts continue to argue privately that air bombardment can do it all, given enough time. Army leaders -- including Gen. Colin L. Powell, chairman of the Joint Chiefs of Staff -- have been warning against counting on bombing to win the war, saying it could come down to soldier-against-soldier to root the Iraqi army out of Kuwait.