Army Apache helicopters and Special Operations Forces troops combined efforts to blast a path through the outer ring of Iraq's air defenses on the first night of the Persian Gulf War, Pentagon officials revealed last week.

The AH-64A Apaches fired Hellfire missiles into two of the air defense command centers, which stood between Baghdad and the first wave of attacking fighter-bombers, the officials said. The Hellfires knocked out the command centers, denying Iraqi gunners near Baghdad time to fire antiaircraft missiles and guns accurately, the sources said.

The United States lost only one plane on that raid, a Navy F/A-18 Hornet. Air Force officials said they had expected to lose between 25 and 40 planes in that first air assault on Baghdad.

The Iraqis "have no idea what happened to them," a Pentagon official said. "They thought they got hit from above {that is by airplanes}, not from below {by low-flying helicopters}."

The Special Forces troops participated in attacks against the two command centers, which were located near the Iraqi border and formed a part of the outermost line of Iraqi air defenses, officials said.

They would not say exactly what the troops did, but acknowledged it would be a standard tactic for them to have helped illuminate the targets for the Hellfire missiles.

A Special Forces soldier on the ground that night, or possibly in a small helicopter that stayed close to the desert floor to avoid detection, was in position to shine laser beams on a command center. Such beams would bounce off the target and form a cone of light in the sky, Pentagon experts said. The Hellfire missile is designed to seek out those cones of light and ride the beams into the source of the reflection -- in this case, the command center.

Although the large Apache attack helicopter can do this targeting, rising off the desert surface would have made it vulnerable to ground fire, Pentagon aviation experts said.

The favored technique is to keep the AH-64A low, preferably behind something like a sand dune, and let it pop up into the sky only long enough to launch its Hellfire missiles.

The Hellfires hit the command centers that first night, sources said, putting the installations out of action. The centers operated Iraq's search radar, which scans the sky for hundreds of miles from the border to warn of approaching planes.

There are more than two such search radar centers, Pentagon officials said, but by eliminating two, the Apaches effectively knocked a hole in Iraq's system and provided the path for U.S. planes en route to Baghdad.

If all the centers in the search radar net had been operating the first night of attacks, Pentagon officials said, they may well have been able to warn antiaircraft installations in the interior that planes were approaching.

The disabled search centers might also have been able to give Iraqi gunners around Baghdad the altitude and bearing of the oncoming planes, making them easier to shoot down.

"I'm amazed we lost so few planes," one Pentagon radar expert said. He said that the Soviet Union has given Iraq excellent search radars -- one version called Tall King and the other Spoon Rest. But they are above ground and vulnerable to intensive bombing, he said.

Gen. Colin L. Powell, chairman of the Joint Chiefs of Staff, said on Wednesday the United States had been attacking these search radars steadily to keep them out of action.

Other radars under attack are fire control radars, used to guide missiles and gunfire into attacking planes. These defenses are also being attacked repeatedly, Powell said, but Iraq has been working feverishly to repair them or improvise alternative air defense systems.Staff writer Jim Hoagland contributed to this report.