WITH U.S. FORCES IN NORTHEASTERN SAUDI ARABIA, FEB. 5 -- The newest disco in the desert opened Monday night in a Marine-issue tent, and the hottest dance on the plywood floor was "the Gas Mask."

To the beat of rock music, the dancers pounded their black boots, waved their arms and mimicked donning their chemical protection masks. "MOPP Level 4! MOPP Level 4!" they chanted as others spun their red-glassed flashlights over the floor like disco lights.

For this communications company of the Marines' Force Service Support Group, the club -- named MOPP Level 4 for the highest state of alert for a gas attack -- provides an opportunity to let off steam and make light of one of the most serious risks in their desert camp just south of the Kuwaiti border: an Iraqi chemical weapons attack.

"We're just having fun, trying to make the best of it," said Cpl. Joey Anderson, 23, of Alexandria. Anderson did a slow rendition of the Gas Mask, illustrating how first you bend over and put your hands to your chin, imitating the proper way of putting on a mask: chin part first.

Then you stand up straight, put your arms at shoulder level and move your fists toward and away from your head, the universal military signal for gas attack.

The guys got the idea for the Gas Mask dance after watching Lance Cpl. Neil Burke, 22, a reservist from New York, run up and down a sand berm in his gas mask and gear one night last week when the whole camp went to a MOPP Level 4.

"I'm over on the top of a hill with my gas mask on and I'm suffering in some serious way," said Burke. "I started flipping ... running back and forth. I always knew how to use {the mask} but I was sweating from running up and down the hill."

MOPP stands for Mission Oriented Protective Posture, and it's the military designation for alert status in anticipation of a gas attack. Four is the level at which everyone in camp must don complete chemical protection gear: pants, jacket, boots, gloves and mask.

Cpl. Lamar Franklin, 23, of Memphis provided MOPP Level 4's stereo system, which he lugged out here to this spartan camp. Franklin doubled as a bartender, passing out soda pop from behind a wooden makeshift bar.

"If you have a big imagination," said Franklin, pointing to the barrel of drinks, "that can be anything you want it to be. Even cans of Budweiser." Since Saudi Arabia is a dry country, this is probably the first war U.S. troops have fought without alcohol.

Franklin was filling in for MOPP Level 4's regular deejay, whose club name is "Scud B" and who was out on a job, said Franklin.

"I'm the bouncer," said Nathaniel Penn, a chunky-biceped lance corporal from Mobile, Ala. "This is more or less a stress reliever," said Penn, 24. "We work so hard preparing for war. We don't take time out at night to relieve stress."

The club's attire is not your usual, and weapons are not checked at the door. Anyone wishing to enter must be in the forward supply camp's 24-hour required dress: helmet, flak jacket, rifle and gas mask.

At this front-line camp, nighttime is governed by what the military calls "noise and light discipline" -- the camp seems like a city gone underground. Off in the distance, you can hear the deep rumble of B-52 bombing runs on Iraqi positions inside Kuwait. And sometimes you can see the orange and yellow flashes from the bombers' huge payloads exploding on the ground.

Monday night, the sounds of MOPP Level 4 broke through the silence of camp. It also brought Maj. John Hand, the communications company commander, bolting through the club's door. "You can be heard over at the COC {combat operations center}," he said. "In fact, you can probably hear you all the way to the Kuwait border."

"Keep it down to a loud roar," he admonished his troops. "Have fun and enjoy yourselves, but {remember} noise discipline." Hand was one of the officers who signed off on setting up the club, knowing that the troops would need some fun out here. But for him, MOPP Level 4 "is not a disco. It's an entertainment tent."

After Hand's visit, there was a lot of "shushing" along with the dancing and laughter. Franklin was vetoed when he announced he was "going to slow it down a little" and put on slow music. "Look at the ratio! Are you kidding?" yelled someone, referring to the male-female makeup of the club's clientele: about 20 men and five women.

Lance Cpl. Vannessa Winborne, 21, of Alexandria, gas mask hanging from her waist, certainly didn't mind the odds. "I'm having fun. I'm always having fun with music," she said.

A phone installed behind the bar can alert MOPP Level 4 to the real thing if necessary. When it rang Monday night, the music cut off and everyone stopped talking. "He was just testing the line," said Franklin as he hung up.

Like most opening nights, MOPP Level 4's had its snafus. Just before the 10 p.m. closing time, Burke was demonstrating how one of his mates almost knocked himself out on a pole when he came crashing into his tent to announce a gas attack alert.

Burke's demonstration, however, was a bit too real. He bumped against the club's tent pole and it came tumbling down along with half of the club.

But MOPP Level 4, the Marines promised, would reopen for business the next night.