The mysterious tunnels of Iraq are rumored to stretch for scores of miles, linking palaces, military strongholds and safe houses, and concealing leaders, treasure or weapons of mass destruction.

For U.S. troops strapping on night goggles and venturing underground, the tunnels are a new kind of battlefield in this war. No maps, no light and no handle - yet - on what they might find.

''For the type of regime we're dealing with, the tunnels represent an ideal spot to conceal weapons and serve as a hideout and in some cases an escape route,'' said Lt. Mark Kitchens, a spokesman for U.S. Central Command.

Saddam Hussein is said to have built so many tunnels that just about anything could be underground - troops, weapons of mass destruction, the Iraqi president himself.

''There were all sorts of tips and rumors, 'dig under this and you will find that,''' said Ewen Buchanan, a spokesman for the U.N. Monitoring, Verification and Inspection Commission.

Buchanan said U.N. arms inspectors in 1998 found a combination of bunkers and tunnels below some of Hussein's palaces, but not the sophisticated network that had been speculated about.

''But that doesn't say that they don't exist,'' he said.

On Tuesday, at the airport outside Baghdad, 150 soldiers of the 101st Airborne's 3rd Battalion, 3rd Brigade searched a 12-room complex inside a cave with white marble floors, 10-foot ceilings and fluorescent lighting. They found cigarette butts, tea bags and other signs of recent abandonment - but no Iraqis.

''We're going to have to try to figure out where they go,'' brigade commander Lt. Col. Lee Fetterman told Associated Press writer Kimberly Hefling. ''There's no telling.''

On Monday, U.S. forces captured an Iraqi colonel in one tunnel who was calling in artillery fire from his hideout.

Also at the airport, a Knight-Ridder news service report described 30 men from 1st Platoon Apache Company entering a tunnel through a ''Staff only'' doorway below the airport's baggage claim. They found a corridor 20 feet high and 20 feet wide that stretched for hundreds of yards in each direction - but no Iraqis.

Reports, some stretching back years, allege the existence of tunnels and bunkers built by Serbian, German or Chinese engineering firms, leading from palaces to secret hideaways and more.

Defense Secretary Donald Rumsfeld repeated those claims in December, arguing the futility of U.N. searches for weapons of mass destruction.

''They've got enormous miles and miles and miles of underground tunneling,'' Rumsfeld said. ''I don't know how inspectors on the surface of the Earth can even know what's going on in the underground facilities.''

Hussein al-Shahristani, a scientist who was imprisoned by Saddam and fled during the 1991 Gulf War, told CBS' ''60 Minutes'' in February that plans originally called for a subway beneath Baghdad.

Hussein ''got all the drawings; he told his military, 'Go ahead and do them but not for a metro, for our weapons of mass destruction. We can hide them, move them around,''' al-Shahristani said. ''We believe now it is more than 100 kilometers (60 miles) of very complex network, multilayer tunnels.''

But al-Shahristani never saw the tunnels himself, he said.

Few have, said Patrick Garrett of Globalsecurity.org, a military affairs think tank. ''There is tons of conjecture on this subject right now,'' he said, but ''there's been no official confirmation or official imagery.''

After encountering the caves used by al-Qaida and the Taliban in Afghanistan and the rumors of tunnels here, the U.S. military took steps to ready their troops.

A 1.1-million-acre site with miles of old mining caves in the Mojave Desert in Southern California was turned into a Tunnel Warfare Center in 2001, training troops in the challenges posed underground.