The rules for a cave assault: Strike fast and hard, keep the enemy off balance, use four-man teams and advance quickly from room to room.

A U.S. military expert said those are the type of tactics likely to be used by American commandos and anti-Taliban Afghan rebels advancing on the Tora Bora and other cave and tunnel complexes where Usama bin Laden and other Al Qaeda leaders are suspected of hiding.

"We try to rely on speed," says Army 1st Sgt. Alexander Somoda, a Ranger and combat veteran from Panama and Iraq who now trains infantry troops in urban combat at Fort Lewis, Wash. "You want to hit them hard. You knock him back on his heels."

Laying out the tactics for an assault, he says to watch for traps once inside a cave and prepare for casualties — it's hard to miss when armed men are shooting at point-blank range.

"If the enemy is very clever, there's a certain point you're going to lose a few people," says Somoda, who trains infantrymen in urban combat in one of the Army's new lightweight brigades at Fort Lewis, Wash.

An estimated 1,500 Afghan tribal fighters, aided by U.S. commandos, are advancing down a valley near the Tora Bora complex in the White Mountains south of Jalalabad.

It's unclear how much close-quarters instruction that U.S. forces may have provided, but it's among the things Green Berets are trained to give, Army Special Forces spokesman Maj. Gary Kolb said.

Much of America's high-tech superiority would be lost in a direct cave assault. No air support, no computers, no satellite aid. Caves are too dark for night-vision goggles to be effective. The troops must rely on gun-mounted flashlights to see.

To some, waiting out members of the Al Qaeda network is a safer course of action.

"They should lay siege, rather than go in and fight for every inch — it's not worth it," said Ali Jalali, a former Afghan colonel who fought with the mujahedeen against the Soviet Union.

An Army company — about 150 soldiers — would be assigned to a cave complex. After confronting guards outside the cave, the unit would then move to isolate the entrances, preventing escape and reinforcement.

Stationed outside, soldiers with mortars, heavy machine guns and sniper rifles would fight off any approaching enemy forces. Then, squad by squad, the rest of the team would go in.

A nine-man squad would advance toward a particular section of the cave. Most would have a smaller version of the M16 assault rifle. Two troopers would have heavy-duty automatic rifles with magazines holding 200 rounds. Two more would have rifle-mounted grenade launchers. Special operations commandos also would have shotguns.

Somoda says the goal is to move swiftly and prevent the enemy from organizing. But as the soldiers advance, they risk triggering a trap — probably a tripwire that springs a grenade.

He advises his troopers to stay alert, watch for anything that catches their eye: "If there's something that makes you look up, you better look down."

Tossing stun or explosive grenades is extremely dangerous. The concussion from the blast could hurt U.S. and allied troops, and cause an avalanche of stone. The Soviets used chemical warfare extensively to roust mujahedeen from caves during the 1980s, but many U.S. infantry units are not equipped with such weapons for high-speed assaults.

Instead, Somoda says a four-man team would assault a room — rushing in one at a time, assigned to different parts of the room.

Once the shooting stops, the team checks to make sure no member is hurt and moves on to the next room.

Soldiers would guard intersections and passageways and leave lighted markers to alert new squads which areas have been cleared.

While U.S. intelligence officials are skeptical of reports of the massive underground complexes, they describe small networks of caves, chambers and hallways built into several mountains outside Jalalabad.

Some of these redoubts were financed with CIA money during the mujahedeen's uprising against the Soviet Union.

U.S. intelligence believes Al Qaeda has between five and 10 mountain hide-outs in the area like the Tora Bora complex, but has little information on the layout within. In addition, hundreds of natural caves dot ridgelines and mountainsides.