It is 1:30 p.m. and the Red Cross hosptial tent at this huge refugee settlement is about to reopen after a break for lunch. Outside dozens of sick Cambodians -- old men, children in ragged shirts, women with sniffling babies -- are already waiting in the sun for the doctor's call.

At the door to screen patients is Jean Meyer, a 28-year-old nurse from Wheaton, Md., who signed up with the Swiss-based International Red Cross last year to come to Tahiland as a volunteer.

In December she was assigned to Camp 204's dirt-floored hospital tent. Located just 10 yards from the bed of a stream that is believed to mark the start of Cambodian soil, it is in a truly forward area where the sound of border shell-fire -- sometimes only a mile away -- is heard.

"A lot of them, have coughs and worms," says Meyer after bending close to a somnolent infant clutched to its mother's breast. Here, as at other border camps where close to half a million Cambodians have massed in recent months, the biggest concern for a doctor is not wounds but diseases like these, which are easily treated if basic drugs are available. b

In a mixture of French and good-natured sign language, Meyer directs patients inside, where doctors sit at consultation tables strewn with pill bottles. One of the doctors is James Cobey, an orthopedic surgeon with a private Washington practice at 19th and I Streets NW.

He is dressed in a dust-covered suit of work clothes and his eyes show the strain of the long hours worked at border clinics. Like Meyer, Cobey left the United States and came to Thailand for only expenses and a 45 Swiss franc (about $27) per diem.

Three months of rice shipments from the United Nations and Red Cross have worked wonders on the average refugee's physical condition. For the time being, at least, one doesn't see the scenes so common in October and November, when doctors worked feverishly but still lost dozens of patients daily to starvation, malaria and dysentery.

Still, the Red Cross medical team -- it numbers about 25 people -- has plenty to do when it arrives at Camp 204 each morning. Together with smaller units from France and West Germany, they provide medical services for a camp estimated to hold 200,000 people.

Last month about 400 patients showed up daily. Most walked in, but a few -- like an old woman bundled up in a hammock slung from a pole that two men carried over their shoulders -- arrived too weak to move.

Meyer and a Candian doctor quickly laid her out on straw mats that serve as beds, took her pluse and listened to her heart and breathing. Questions posed through a French-speaking Cambodian revealed she was running a high fever and had heavy diarrhea -- very common symptoms among Cambodians.

The Red Cross tent offers medicine at its most basic, hardly what Meyer and Cobey practice at home. Meyer has worked in up-to-date facilities such as the Washington Hospital Center. Dr. Cobey normally performs bone surgery in a modern operating theater.

"My first days here I was doing surgery in grass shacks," Cobey recalls. With no laboratory or X-ray facilities, there is no room for fancy diagnostic work. "You try to make the greatest impact on the simplest things," the doctor explains. "It's no use diagnosing cancer of the colon."

Occasionally a gunshot case is carried in. Only a few miles inside Cambodia the right-wing Khmer Serei (Free Khmer) guerrillas who run Camp 204 are harrassing Vietnamese forces deployed to support the year-old Heng Samrin government in Phnom Penh.

Camp 204 itself could become a combat zone if the Vietnamese mount a major offensive to clear the border. Medical agencies have taken the precaution of drawing up evacuation plans and building roofed bunkers with passageways leading into the Red Cross hospital tent.

Shooting also might come from the Thai side of the frontier. On one recent morning 204's German medics were late arriving because Thai troops were firing mortars at Free Khmer guerrillas sighted a few hundeds yards off the route to the camp.

Both Cobey and Meyer are quick to admit that altriusm is not the only factor behind their presence at 204. Cobey, with experience in field medicine in the Gaza Strip, Haiti and Nigeria flatly states: "I enjoy this kind of work."

Meyer says she loves it too. She decided to come after a discussion with other Washington nurses about the humanitarian versus the monetary rewards of nursing. But, she adds, she was also looking for a chance to get into international medicine.

So, after arranging for payments on car and school loans, she signed up for three months in Thailand and may well extend. Assigned to a six-member team that included Cobey, she received lectures on tropical medicine and how to react in the event of an attack before coming to Camp 204.

The hospital tent closes up before dusk and the team returns to a tent city the Red Cross maintains well back from the border for its medical workers.