The medics are at the front lines, the MASH units have been set up, and thousands of military doctors and nurses are waiting tensely for what could be the most grueling test of their ability to care for wounded soldiers since World War II.

The system of clinics and hospitals now in place in the Gulf is "of a size and complexity that would supply the city of Seattle," said Brig. Gen. Ronald R. Blanck, chief of medical corps affairs for the Army Surgeon General.

A major ground battle between allied forces and Saddam Hussein's troops will stress the combat-readiness of a military medical system that, for the last two decades, has had to deal largely with peacetime injuries.

"Sometimes, we don't pay enough attention to training for war -- the differences in medical practices and being familiar with field conditions," said Blanck.

No matter how much experience military doctors may have had in busy urban emergency rooms, he added, "it still isn't the same. It still isn't like what you see over there. But short of being in a war, I don't know how to train for that."

Because a ground war in the Persian Gulf means a confrontation between two large armies, backed by artillery and fighting in a treeless desert, Army officials say, it would likely result in much larger numbers of casualties, occurring within shorter periods of time, than the battles of either the Vietnam or Korean wars.

The medical planning for the war is based on classified casualty estimates. But Blanck said the Army's estimates are substantially lower than the estimates of 10,000 dead and 35,000 wounded recently released by the Center for Defense Information, an organization of retired military officers often critical of the Department of Defense.

"We've worst-cased it," said Blanck. "The worst-case scenario would be a theater-wide attack of artillery and armor, with air support, on relatively unprotected troops."

To handle such a scenario, he said, the military services have spent the last six months setting up a medical system in the Gulf that now includes more than 10,000 hospital beds staffed by the Army -- including both field hospitals and "host country" hospitals in Saudi Arabia, Oman and the United Arab Emirates -- plus more than 3,500 beds operated by the Navy and a smaller number staffed by the Air Force.

More than 46,000 medical personnel have been activated from the military reserves. As a result of the call-ups, the ranks of military doctors have swelled to more than 16,000 today, with about 20 percent stationed in the Gulf region, Blanck said. Blood, antibiotics, nerve gas antidotes, chemical decontamination kits and surgical instruments are flowing to the Gulf daily by plane and by ship, tracked by a computer system that is supposed to alert officials automatically whenever supplies of a particular item start to run short.

The Army has even deployed two mobile CT scanners -- sophisticated machines that provide computerized cross-sectional images of the brain and other internal organs -- to its field hospitals in Saudi Arabia.

Blanck said that when Operation Desert Shield began last August, the Army was gradually converting its field hospitals from outdated Vietnam-era equipment to a new kind of modular hospital called DEPMEDS (for deployable medical systems). DEPMEDS, which are made of standard-sized boxes and tents that can be linked together like Legos to make a field hospital of any size or layout, are now being used by all the armed services.

But Blanck acknowledged that many military medical workers have had little experience with the new equipment. "Since we've paid so much attention to peacetime care, we've not done enough in training to familiarize our health care folks . . . with field equipment in the field environment," he said. He said that most of the Army's doctors, nurses and paramedics have taken a 10-day course in combat casualty care, and many have had several months in Saudi Arabia to get used to the new equipment.

The military's routine for taking care of wounded soldiers depends on moving them rapidly through a system that provides graduated levels of increasingly sophisticated care. It starts with rapid first aid and transport at the front lines and progresses to an array of larger hospitals located behind the lines.

The first person to help a wounded soldier would likely be a "combat lifesaver," a fellow soldier trained in advanced first aid, Blanck said. Next on the scene would probably be a medic, a soldier trained as an emergency medical technician, with the skills needed to start an intravenous line and perform other resuscitation procedures.

Blanck said the wounded soldier would then be moved to a nearby battalion aid station, located in a tent or a "Bradley," the military nickname for an armored personnel carrier. There, the soldier would be checked by a doctor who could start to treat his injuries, administer more intravenous fluid, and, if necessary, insert a tube in his throat or chest to help him breathe.

From there, the patient might be transported by air or land to a "clearing company," a larger medical station set up in tents a half-mile or more behind the lines. Doctors there, usually trained as emergency-room physicians, can administer drugs, perform minor surgery and keep patients on cots for as long as a few days. Blanck said soldiers suffering from minor wounds or from short-term combat-related psychological stress often can return to duty after a short stay at the clearing company.

Someone with more serious injuries could go directly from the battalion aid station to a Mobile Army Surgical Hospital, or MASH, a 60-bed surgical intensive care unit located half a mile or more behind the lines. MASH units have mobile X-ray equipment, can provide basic laboratory tests and have teams of surgeons standing by to perform emergency trauma surgery.

Alternatively, wounded soldiers or those with non-surgical illnesses, such as pneumonia or severe combat-related stress reactions, can be sent to a combat support hospital, or CASH, a 100-bed hospital that has internal medicine specialists and psychiatrists as well as surgeons. Still farther behind the lines, there are 200-bed Army field hospitals and 400-bed evacuation hospitals (EVACs) that provide similar services, plus additional, more specialized treatments like emergency neurosurgery.

Blanck said that, under the military's medical "triage" -- injury assessment -- system, there is a limit to how long a patient can remain at each level. In a MASH unit, for example, patients can be kept no more than 72 hours. Anyone too sick to return to duty must then be moved on to a larger hospital or evacuated to Germany. The decision to evacuate a seriously ill patient can be made at any point in the system, he said.

"The point is, keep the flow moving and keep beds open," he said. He added that teaching doctors and nurses how to make such triage" decisions is the hardest part of combat medicine. "It has to do with experience. Until you've been in the situation, it's tough."

In addition to the Army, the Navy has established three 500-bed land-based "fleet hospitals" in the Gulf region. It also has two hospital ships, each with 1,000 beds.

The Air Force has set up a number of 50-bed hospitals, similar to MASH units, near its air bases and provides the specially equipped medical evacuation planes that fly sick or injured patients from all the services to military hospitals in Germany.

Members of any service can be treated at any of the hospitals. "It's very much a cooperative effort," said Lt. Joy Hopkins, a Navy medical spokeswoman.

All patients evacuated from the Gulf region will go first to Germany, then to military hospitals either elsewhere in Europe or in the United States. Veterans Administration hospitals may also receive war casualties if the military hospitals fill up.

Blanck said that, although the system can probably handle most of the burden, there could be a critical shortage of "burn beds" if large numbers of soldiers suffer burns.

"We can provide initial burn care," including fluids, pain relievers and measures to prevent infection, he said. But long-term care of burned patients requires weeks of rehabilitation and, often, extensive surgery.

Brooke Army Medical Center near San Antonio, the Army's primary burn hospital, has 40 burn beds and can only expand to about 125. There are only 2,028 burn beds in the United States, according to the American Burn Association. "If we get lots of burns, that would be a problem for us," said Blanck.

Doctors at military hospitals here, as in the Gulf, already are preparing for the worst. At the Uniformed Services University of the Health Sciences in Bethesda last month, about two dozen orthopedic surgeons from Walter Reed Army Medical Center, Bethesda Naval Medical Center and other hospitals in the region spent a Saturday morning operating on cadavers, practicing the technique of inserting a new type of metal rod that allows patients with fractured spines to move around much sooner than older devices.

A course on how to use the new rod had been planned for the spring, but the date was hastily moved up after Operation Desert Storm began. During breaks, the surgeons avidly scanned newspaper accounts of the war.

"This is what we do," a doctor from Bethesda Naval Medical Center said of the spinal surgery. "But all of a sudden, instead of car accidents, it's . . . ," He left the rest of his sentence unfinished.