Plantains and mangoes are not Carol Budi's real business, but when the Haitians rushed from their bleak barracks to meet the van rolling in the other day from Baltimore, full of those tropical staples, she acted like the proudest merchant in town.

Budi is a nurse-practitioner, a nurse who diagnoses and prescribes for patients, not a mango vendor. But medicine as it is practiced farm worker camp near the town of Princess Anne is something else again.

It is tropical fruit, antibiotics, fear of guns. It is threats, awesome worms in children's stomachs, filth. It is angry farmers, abysmal camps, fear of epidemic.

Budi decided that one way to combat the depression and hypertension so common among the Haitian field hands was to provide some foods they were accustomed to. With Department of Agriculture approval for the use of food stamps, she set up a buyers' co-op for the workers and a happy ray of mangoes and plantains beamed down on Westover.

That was a bright spot, but others are less so.There was the time Sister Jane Houtman, another nurse, was run off the road by a resentful migrant crew leader. Last year a crew chief brandished a gun in front of another nurse from the Delmarva Rural Ministry. And this summer, farmers ejected Budi and her crew from the Westover camp. Confrontations are common events, fear a constant companion.

That's the way it is in the farm labor camps on the Eastern Shore of Maryland, Delaware and Virginia and it is a special kind of medicine these nurses are practicing, a special kind of patient they are treating.

An estimated 6,000 or more migrant farm laborers have worked the vegetable and fruit farms of Delmarva this summer and many of them have been touched by the nurses and volunteers who staff four clinics the Rural Ministry operates.

The migrant health and legal aid programs that are funded with federal grants have caused controversy nationally, as they have here on the Eastern Shore. But in many instances those services, now ticketed for funding cutbacks by the Reagan administration, are all that stand between the migrants and desperate illness or deprivation.

To hear Budi or Sister Regina Hudson, who supervises the Delmarva migrant clinic at Nassawadox, Va., recite the infirmities found in the labor camps in their areas is to hear a catalogue of infirmity more common in the underdeveloped world: Active tuberculosis, veneral disease, ear and upper respiratory infection from the dirt, dermatitis, hypertension, diabetes, parasites, endemic diarrhea.

Budi's experience with migrant health has taken her to camps in New York and Wisconsin. "This place [Westover] takes the cake," she said. "This camp could not exist in Wisconsin. The laws are tougher."

One of Budi's special causes in recent weeks has been an 8-year-old Haitian boy with an abdomen severely distended from parasitic infection. Tests disclosed a massive collection of worms in his body. "These things make me think I'm in the Third World," she said. "I woke up last night just thinking about that boy."

Nurses and medical aides on the Eastern Shore attribute many of these problems to the lack of sanitation in the camps. But even though dirty water, open garbagek containers and inadequate sanitary facilities are common, the camps pass minimum state and county standards with little or no difficulty.

"Migrants are very special people, with very special needs," Budi said. "Nobody attends to them, so you feel compelled to help them while they are here."

Not that this is so easy. Local resistance to nurses from the clinics and the lawyers and the paralegals from the migrant legal aid centers on the Eastern Shore makes the task more difficult. Health and legal workers, often barred from some camps, say they are made so uncomfortable when visiting that they prefer to deal with patients and clients in neutral settings.

Charles Bruce, head of the Somerset County growers' group that operates Westover, complained that migrant-health nurses, particularly Catholic nuns from the order of Daughters of the Holy Spirit, have "agitated" to stir antagonism toward the farmers.

"They haven't made things very nice for us," Bruce said. "They've gone way beyond providing health care. We don't even know how many workers are in the camp -- but they do. They go around with yellow pads, knocking on every door. I say they were checking on us as managers of the camp."

Migrant legal-aid workers have their problems, too. "Through threat and inti0midation, the crew leaders frighten their workers from talking to attorneys about cases of physical abuse, underpayment of wages and the like," said Michael T. Robinson, head of the legal aid center in Belle Haven, Va. "We try to get the workers off the camps, distribute our cards to them and we let them call us collect if they are having trouble."

Another factor in the mix, however subtle, is that growers in some places are important politically. The operators of the Westover camp include a Somerset County commissioner and a state delegate, R.C. Biggy Long. Another nearby camp is owned by a state Democratic central committeeman.

In Virginia, the state commission on migratory labor is headed by Philip McCaleb, who also is president of the potato and vegetable growers in Northampton and Accomack counties. Inland toward the Shenandoah fruit country, the family of U.S. Sen. Harry F. Byrd Jr. (Ind.-Va.) operates a camp for migrant apple pickers.

So it goes in places like Westover, which, with a capacity for an estimated 700 workers, is the largest of the camps on the Delmarva Peninsula. Treating the workers is one thing. Being allowed to treat them is still another.

In July the nurses operating their clinic in a ramshack old barracks building at Westover were told by the farmers that they would have to vacate. The building was needed to house more migrants, they were told. It was too bad about the painting and refurbishing the nurses had done their own time. Too bad about the cleaning job they had done. So the nurses moved into a trailer hastily toward to a site outside the main camp, yet still on the growers' land.

Migrants never occupied the barracks after the nurses left. Bruce said that was because the workers did not show up. But there's more. He said that next year, because of their ""agitation," the nurses will not be allowed into the camp -- nor will they be permitted to set up their clinic on the perimeter.