As a pack of reporters looked on, a dozen Marines in combat gear picked their way through the desolate urban landscape, rushing from one stark three-story building to the next while checking for enemy soldiers behind the gray cinder-block walls or the bullet-riddled carcasses of overturned cars.

Suddenly, a sniper opened fire with his M-16 assault rifle from an upper-floor window about 25 yards away on the training grounds at the Quantico Marine Corps Base. Two Marines went down. A photographer stepped around the corner of a building to snap a shot of Marines attending to a fallen comrade. The photographer, too, quickly fell victim, taking a sniper round to the face.

Fortunately for all concerned, the bullets in this exercise at Quantico were nonlethal, chalk-tipped rounds fired from modified barrels that reduce their velocity. For the most part, they splattered harmlessly on the flak jackets, Kevlar helmets and paintball masks that Marines and reporters alike wore to protect themselves.

But the dangers represented by this type of warfare are real. They make up the Pentagon's worst nightmare: having to take a city in protracted house-to-house fighting that minimizes the U.S. military's overwhelming advantages and inflicts heavy casualties.

"This is a good thing to practice, because it's the worst situation you can find yourself in, as a soldier or a reporter," said Army Sgt. 1st Class Edward J. Matthews, who helped guide journalists behind the Marine lieutenants training to be platoon commanders.

"It's the way of the future," said Capt. Eric Reid, the commander of the exercise at Quantico's Military Operations in Urban Terrain facility. "Everybody has figured out that to fight us in open ground is a bad idea, so they'll be drawing us into cities."

The long-planned exercise became part of an intensive training session last week that exposed journalists to the rigors of combat in preparation for "embedding" with military units to report on a possible war with Iraq. More than 50 reporters, photographers and cameramen from 31 U.S. and foreign news organizations practiced chemical weapons countermeasures and first-aid techniques, learned map-reading and navigation skills and experienced simulated attacks, live fire over their heads and other Marine combat exercises.

The training, the first of its kind by the U.S. military, left three reporters wounded in action (a couple with severe knee and ankle sprains, one with minor burns from a simulated grenade). Dozens of others wound up seasick from pitching naval vessels, gagging from tear gas in a chemical weapons "confidence chamber" or exhausted from a five-mile "tactical march" -- under a series of ambushes -- through the hilly woods of Quantico.

Controversy erupted over media coverage of the last day of training when journalists grew concerned that the planned march in full camouflage -- including flak jackets, load-bearing vests, Kevlar helmets and 25-pound rucksacks -- could convey a false impression that they were being trained for participation in combat. Several of the trainees expressed alarm that such images could endanger their colleagues in trouble spots abroad, especially after a news agency distributed a photo of a reporter looking down the sights of an M-16. No training in the use or handling of any weapon was included in the course.

The situation was resolved when both sides agreed that the assembled hacks would march looking less like Marines and more like the unruly gaggle that they usually are. Camouflage, flak jackets, helmets and Marine rucksacks were all optional. Reporters marched in various combinations of Marine and civilian gear, some in baseball caps or with "press" signs taped to their helmets. (This week, Garry Trudeau's "Doonesbury" cartoon strip has featured military-sponsored training for journalists in which reporters are instructed in surviving a battlefield.)

The decision to forgo full military garb did not stop the reporters at Quantico from being "attacked" three times, once after ascending a steep trail known as Cardiac Hill. As Marines hidden in the woods hurled simulated grenades and canisters of white phosphorus to create explosions and smoke, escorts yelled, "Gas! Gas! Gas!" to signal a chemical attack. The marchers dived for cover in the tree line and whipped out their M40 field protective masks.

Richard Sisk of the New York Daily News, a Vietnam War veteran who received two Purple Hearts for grenade wounds, became a casualty once more when flaming material from one of the munitions landed on him during the last simulated attack, burning his left hand.

The training, which included three days with the Navy and four with the Marines, reflected a determination by the U.S. military that it needs to do a better job of accommodating the media in any future conflict. As a result, the Pentagon has agreed to "embed" journalists with military units to provide first-hand coverage.

Not yet resolved, however, is the question of how and when reporters will be allowed to file their stories from the field. Military officials said the use of satellite telephones or cell phones on battlefields or naval vessels could compromise "operational security," notably by giving away locations, but they provided no details on the capability of an adversary such as Iraq to intercept and exploit such transmissions.

The main goal of the training is to "raise the comfort level" of the media and the military, said Victoria Clarke, assistant secretary of defense for public affairs. "And it's a sign of people taking things seriously." She said additional training sessions are planned to meet requests from more than 400 journalists. The next session is tentatively scheduled for Fort Benning, Ga., in mid-December.

To help achieve what it calls "information dominance," the military also announced plans for a new Joint Public Affairs Operations Group that would rapidly deploy teams to future battlefields to interact with journalists, assist U.S. commanders and send news and pictures back to headquarters for dissemination.

The week of training began with a stomach-churning ride in rough seas aboard military hovercraft, called LCACs, to the amphibious assault ship Iwo Jima off the coast of North Carolina. After spending the night on board, the journalists landed at Norfolk Naval Base the next day and visited a nuclear submarine, a destroyer, a cruiser, a Navy SEAL team and the aircraft carrier Harry S. Truman, described by Capt. Michael R. Groothousen, the commanding officer, as "98,000 tons of diplomacy."

A bus ride to Quantico then introduced the group to what Marine Brig. Gen. George Flynn described as a kit bag of survival tools. "What we do is real training," he said. "This isn't a dog and pony show."

Classes at the Basic School, which trains young Marine officers, included mine awareness and combat first aid. Tech. Sgt. Antonio Rita, an Air Force medic, taught the group how to treat sucking chest and open abdominal wounds. Never try to reinsert intestines, he warned. "You don't know where they go, so don't do it."

The journalists later received instruction on various chemical and biological agents. They donned MOPP -- Mission Oriented Protective Posture -- suits and practiced putting on their M40 masks in nine seconds or less. "Why nine seconds?" asked the instructor, Marine Gunnery Sgt. John Shay. "Because in 10 seconds you're dead."

A taste of combat came when the journalists, in full kit, boarded two Marine helicopters to spend a night in the field and were dropped into a "hot" landing zone. Hidden attackers opened up on the group with machine guns (firing blanks), lobbed artillery simulators consisting of quarter sticks of dynamite and threw in some white and green phosphorous grenades to add smoky confusion as the reporters ran with their packs to the landing zone's tree line, hitting the ground every few steps. A New York Times photographer, Angel Franco, didn't make it. He wrenched his knee and ended up on crutches.

At Range 11, groups of journalists followed platoons of Marine lieutenants through a patch of woods and over a marshy draw as the young officers launched an infantry attack using live ammunition. F/A-18 jets, practicing close air support strafing runs on another range, banked sharply in the clear sky. Artillery fire boomed in the distance.

Abdullah Saafin, left, a Palestinian photographer who works for Abu Dhabi TV in Washington, takes cover with other photographers at Quantico. Journalists participate in an exercise with gas masks. The training, the first of its kind by the U.S. military, left three reporters wounded in action; others became seasick on Navy vessels or exhausted from marching. Patrick Van Haute, a Marine from West Chester, Pa., waits for an exercise to begin. The media were invited to the training to help them prepare to cover a war with Iraq.