From his tactical operations center at the airport that he prefers to call Baghdad International, Col. William Grimsley is looking for ways to expand his turf.

Already he controls the military and civilian portions of the airport on the southwestern edge of Baghdad, including a VIP terminal that contains what U.S. soldiers suspect was a hideaway for President Saddam Hussein. Elaborately appointed, it has a thick hand-carved mahogany door, gold-plated bathroom fixtures and a veranda opening onto a rose garden. But its most intriguing feature is a wood-paneled office with a false door that leads to a basement room. There, troops of Grimsley's Army brigade found weapons, but they believe there is something more: a secret exit.

"We're sure there's a way out of it," said Grimsley, commander of the 3rd Infantry Division's 1st Brigade. "We just can't figure it out." But it stands to reason that another concealed passage exists, said the 45-year-old native of Arlington and graduate of McLean High School. "It's a very secretive regime. This is his means of escape."

Shutting off Hussein's means of escape is one of the missions of Grimsley's brigade and other U.S. forces arrayed around Baghdad. By taking up positions on all sides of the capital, military officials said, the units intend to gradually extend the areas they control to put an intensifying grip on Baghdad, a squeeze that commanders hope will result in the fall of Hussein's government.

"If we just sit here and wait for it to crumble, it may never happen," said Capt. Andrew Valles, 27, of Weirton, W.Va., a staff officer at 1st Brigade headquarters. "We'd also be hurting the people by sitting here and starving out Baghdad. So we can't just sit here. We have to expand our presence."

When the 1st Brigade took over the airport two days ago, after a fierce battle to capture it by forward units, troops found it heavily damaged by airstrikes and mostly deserted. The hulk of an Iraqi airliner, still smoldering from a direct hit, lies on the tarmac next to a huge protective embankment. Airport hangars, now bristling with antennas, bustle with the activity of military planners.

An airport warehouse complex has been reduced to ruins. Runways and aprons serve as parking and maintenance areas for U.S. armor. As brigade staff officers went about their business, the crew of an M1 Abrams tank with the name Bad Boyz on its gun barrel worked to fix a mine-clearing plow on the front of the 72-ton behemoth.

After arriving before dawn, a platoon of M2 Bradley Fighting Vehicles from the 2nd Brigade that escorted a convoy of multiple-rocket launchers, ammunition trucks and other vehicles to the airport area stopped on a runway and disgorged its infantrymen. Exhausted by a sweat-soaked ride packed inside their Bradleys, a stop-and-go trip that took 10 hours to cover 30 miles, the soldiers spread out sleeping bags on the tarmac and caught a few hours sleep.

The trip was otherwise uneventful, but a foray by another pack of M1 Abrams tanks through the southern suburbs of Baghdad on Saturday met both resistance and well-wishers. "Half the people were standing there cheering and waving, and half were shooting at them," Valles said.

Some of the shooting of rocket-propelled grenades and small arms came from people in civilian clothes, while others wore military uniforms, he said.

The drive, by the 2nd Brigade's 1st Battalion, 64th Armor Regiment, took the column along Highway 8 and under a huge, arched sculpture of sabers in what are meant to be Hussein's hands. Grimsley described the movement as a "reconnaissance in force" intended to "determine the trafficability and the level of resistance" of that route, which links two of the 3rd Infantry Division's strongholds on the southern edges of Baghdad.

"Also, it was a great demonstration of our capability," he said.

The dash by U.S. armor through southern Baghdad was carried out "just to prove that we could do it," Valles said.

Resistance at the airport has been sporadic, consisting mostly of occasional artillery rounds, officers said. At a blocking position east of the airport, a battalion of the 1st Brigade has come under more consistent fire. "There's been lots of sniping and stray RPG [rocket-propelled grenade] rounds," Valles said.

Including a suicide car bomb attack that killed four 1st Brigade soldiers on their way north to the airport, the brigade has suffered 12 killed and 40 wounded so far in the 18-day-old war, Grimsley said.

"We continue to find isolated pockets" of fighters, Grimsley said. He said his troops killed a colonel in the Special Republican Guard, an elite force assigned to protect Hussein, after finding him in a bunker dug between two of the civilian airport's runways.

The Iraqi had night-vision goggles, binoculars, a radio telephone, maps and a newspaper article extolling the Sept. 11, 2001, terrorist attacks against the United States, Grimsley said. He said the officer was apparently serving as a spotter for large-caliber artillery rounds. The Special Republican Guard's secretariat headquarters stands about 21/2 miles east of the airport.

In clearing the airport, U.S. troops have found tons of weapons and ammunition, Grimsley said, including four school buses packed with arms and explosives.

"We're going to have to demolish them," he said. "We don't know if they're booby-trapped."

The troops also discovered an underground driving entrance into the VIP terminal, Grimsley said. But "we're still looking for underground personnel tunnels."

The airport is secure and is being used by U.S. helicopters, the colonel said. The first C-130 Hercules transport plane landed here today, officers announced. Troops also are working hard to restore power and water. Grimsley, meanwhile, looks forward to another milestone in transforming Saddam International Airport to Baghdad International.

"The real key will be [the] first civilian plane to land here," he said.

An unidentified soldier from the Third Infantry Division is on the front line of the Army's advance on northern Baghdad while fires burn in the background. An M1-A1 Abrams drives over a disabled vehicle as the soldiers from the Task Force 2-69 Armor, 3rd Brigade Combat Team, 3rd Infantry Division move on Baghdad.