"Tortilla!" snapped Sgt. Jay Dodge, 25, a howitzer battery section chief, to one of his privates. "Pass down the wrap rounds." And, like syncopated ants, the men began piling huge howitzer shells into place.

Stenciled on one was this message: "This one's for the ayatollah."

"Fire mission!" Dodge shouted. The war was on.

It went smoothly at first, this experimental war in the Mojave Desert. The president had dispatched 6,000 Marine desert rats-in-training to this approximation of a barren piece of the Persian Gulf region outside Twentynine Palms, Calif. The script said the Soviet-backed Elon People's Army had seized a chunk of disputed desert from a friendly Arab emirate.

But more than script was at stake in this weekend of pretend war. The Marines of the 7th Marine Amphibious Brigade (MAB) have been earmarked in real life as shock troops who would be used for desert armored warfare in the new Rapid Deployment Force strategy. This was a test, but the bullets were real.

The first day was reconnaissance. On the second, armor and infantry working together wiped out several small enemy units. Then, massed tanks and men, backed by air support, wiped out the enemy force holding a key mountain pass.

The Marine pilots were on target, and the engineers blasted an enemy minefield, giving American tanks safe passage to rout enemy armor, according to Brig. Gen. H. G. Glasgow, commander of the brigade.

But the tank commanders leading the attack had trouble reading their maps, maneuvered beyond the 25-mile radio range and lost communications with their artillery support.

Then came what planners hoped would be the Saturday night massacre. For three days thousands of men had been eating sand and fighting skirmishes from rock to rock. Now, as darkness fell, they dug in, daring the enemy armored column to come through the mountain pass.

Suddenly, the howitzers boomed, echoing off the Bullion Mountains as Marine pilots swooped their F4s into dives to unload cluster bombs of napalm. American tanks shook the earth, their turrets spitting red tracers into the night. Rattlessnakes and gopher turtles scurried for cover as 81mm mortars hit and white phosphorous illumination rounds silhouetted the imaginary enemy on the desert floor.

All at once 700 Marine infantrymen clicked off the safeties of their M16s and, at the sight of the green signal flare to open fire, built a wall of metal. Nostrils twitched from the acrid aroma of cordite, the incense of war, and the cold night was filled with shouts.

"Beautiful!" screemed Pfc. Tom Armitage, 19. He burrowed into his foxhole and imagined he held the ayatollah in the crosshairs of his M16. It jammed. He cursed, and a buddy covered him.

Earplugs help, but no one escapes the first baptism of shock and wonderment at the furies unleashed by a 155mm howitzer, a giant cannon that booms football-sized projectiles seven miles across the heads of advancing Marines. The shells can be set to explode in midair, raining tiny pieces of metallic death on enemy soldiers, or to detonate upon impact, leaving the desert looking like the surface of the moon.

From afar, the shells explode in silence, kicking up black tornadoes of sand. What seems like minutes go by, then comes the rolling thunder, echoing off the mountains, rattling the earth, and giving Marines like Cpl. Tom Bowles, 25, a former St. Louis cop, a tingly feeling all over.

Bowles stood beside his communications truck with a ringside seat at the war. The exploding howitzers filled the air with burned gunpowder.Bowles sucked in the fumes with gusto and sipped from a mug of coffee. "Cordite kind of adds a little tang to your instant coffee," he grinned.

It was cold and grimy inside the armored troop carrier -- "the Hog," the men finally called it -- and it lurched and whined and spewed diesel fumes over the rocky desert, in and out of gullies and dry river beds, making its way to the front, trying to catch up to its unit after a hydraulic system breakdown.

Speeding through the desert at 10 mph, 1st Lt. Dave Shelton, 26, a UCLA graduate and "hog" commander whose father had earned Navy bomber wings the day World War II ended, said he didn't want to miss the live fire assault, or the next war. "It's going to be one hell of a show," he grinned.

The faces of his men were covered with dirt, but they didn't seem to mind. "Sand has a pleasant taste," said Lance Cpl. Brian Jackson, 22, of Baltimore.

"Arf! Arf!" they barked as they rolled past grunts doomed to the rear. They had the ayatollah on their minds. "Pretend you're in Iran," one private said an officer had told him.

They were a bone-weary lot who groused about the food, captured rattlesnakes, gophers and rabbits to ease the boredom, and said they wanted nothing better than to build sand castles in Iran. "Iran owes us," Jackson snarled. "And we owe them a serious a-- whipping. Iran can stand by if we ever get the word."

There was Sgt. Bill Bruder, 25, of Baltimore, who passed out thousand-round belts of machine cartridges to his troops and then showed a reporter how to render a can of C rations -- boneless chicken with cheese sauce -- edible.

There was Laukton Rimpel, 24, a rifle team squad leader and one of eight children born to a Haitian truck driver who immigrated to New York after his wife was gunned down by government troops in Haiti. He said he wanted nothing more than a career in the corps. He'd packed eggs in New Jersey for $2.65 an hour, worked his way through high school, joined the Army, then transferred to the Marines because "he wanted more discipline." He made a corporal in 22 months.

"When we charge out firing, we've got to imagine the enemy is firing back from a bush or a rock," he said. "Otherwise, it's just a game. You won't do it right unless you think someone is out there shooting at you."

On base, he keeps mostly to himself, sending his wife half the $900 a month he earns. He socks away the rest, and plans to retire after 20 years.

"If I'm still alive, I'll be pretty well off," he figures. "A lot of people in the military don't like to take orders, but I don't mind. That's what the Marines are all about, to make somebody out of you."

And there was 2nd Lt. Bill Fitzpatrick, 27, a former cabbie and corrections officer with a Boston drawl, who said, "My troops enjoy the idea of being paid killers. The only thing we're missing out here is the enemy. If we could only get the Iranians to occupy this desert, we'd have it made."

"All right," Sgt. Bruder shouted. "Let's dig some Marine Corps condominiums."

And the troops reached for picks and shovels and began turning the desert into foxholes.

"I'd rather drink beer and watch the Super Bowl than go to war," Lt. Shelton said. "But if we ever do go, we'll kick some a--."

And what if he found himself in the oilfields of Iran, outnumbered by Soviet troops, as military theorists suspect might happen in such a showdown? He shrugged. "That would just give us more targets. There'd be a lot of dead Russians."

On the fourth day, Sunday, the Marines pulled back in a planned withdrawl, beating a dusty retreat to get back in time for the Super Bowl. In the confusion they got outflanked by the enemy's fast, light assault vehicles and took it on the chin.

"Our force did nor fare very well on the last day," Gen. Glasgow said. "The enemy hit our command post and was able to outflank us with helicopters and fast assault vehicles. We lost about one-fourth of our armor and 15 percent of our men. That's more than we'd like [to lose]."

It was the first time the Marines had tried to move armor and infantry together at night in a desert exercise, coordinating their battle plan with close-in air support, then withdrawing from an enemy highly trained in Soviet armor doctrine, Glasgow said.

What he'd learned, he said, was that the 7th MAB needed more detailed planning to coordinate armor and infantry -- and that several of his officers who tried to stay awake for four days needed more sleep. Other officers said they were pleased to learn that light experimental attack vehicles, leased from Canada and used for the first time in these exercises, can be used effectively against slower, stronger tanks.

"We have a lot of work to do to become combat-ready," Glasgow said. But things could have been a lot worse, he added. Morale was high. The Marines found they could supply the troops adequately, and the Marine pilots coordinated well with the ground attack troops, "delivering their ordnance right on target."

"It might look like an expensive fireworks display, but if you don't give the troops training with live amunition and artillery fire overhead, they'll never know the tension of combat," said Col. Robert Wakefield, 44, the lean, sunburned, attack commander who was trying to translate his two tours in the Vietnam jungle into desert warfare. "This is as close as they'll get to the real thing without someone shooting back. If we'd had this experience before Vietnam, we would have lost fewer men."

The Marine Amphibious Brigade is a key player in the controversial 10,000 man Rapid Development Force. No military organization in the last several decades has had "more speculation about its birthright" than the RDF, said Marine Lt. Gen. P. X. Kelley, the confident, 6-foot-4 task force commander of the RDF who swooped in for several hours to observe the battle. tiger," Kelly said. "But the RDF has been tasked with most difficult assignment I've ever heard of in my experience in the military: to project . . . power 7,000 miles away and and sustain it [against] the Soviet Union. That causes one to have a few sleepless nights, but we're getting there as rapidly as we can."

Whether or not the RDF is combat ready, Kelly reminded reporters who shivered inside a green desert tent, the RDF is all America has, with the 7th MAB as the cutting edge for a kind of armored desert warfare that might be required to defend the Iranianoilfields against a possible Soviet invasion from Afghanistan.

Asked if it is a credible force, Kelly said, "Credibility is in the eye of thebeholder. We have the life capability to get there, and could get the leading edge in two or three days. But whether that is enough to deter, well, deterence is in the other guy's mind. This is a high-risk business, and the RDF is the only option we have at the moment."