The United States has begun airlifting relief supplies into eastern Sudan to help feed, clothe and give medical assistance to tens of thousands of malnourished Ethiopian refugees who recently have walked out of the drought-scorched provinces of Tigray and Eritrea.

The airlift, ordered by President Reagan as a response to an emergency appeal from the United Nations High Commissioner for Refugees, began last weekend when a U.S. Air Force C141 cargo plane carrying portable water tanks, 3,200 blankets and six hospital tents was dispatched from West Germany to Sudan.

On Christmas Eve, a shipment of measles vaccine for 24,000 people -- to help stop a measles epidemic in Sudanese refugee camps -- arrived in Khartoum. On Christmas Day, another Air Force cargo plane dispatched from Baltimore arrived in Khartoum with more water tanks and plastic sheeting for tents.

The airlift, according to M. Peter McPherson, director of the U.S. Agency for International Development, is an emergency response to "a crazy situation" created by the influx of 100,000 Ethiopians since September into Sudan, a drought-affected country which is having trouble feeding its own people.

Between 1,200 and 1,500 refugees are flooding daily into the three makeshift camps that have sprung up in the past four months along the Sudanese-Ethiopian border, according to the U.N. refugee agency. The agency says the refugees, some of whom have been walking for up to 30 days, arrive in the Sudan with no possessions, malnourished and in extremely poor health.

The number of refugees has accelerated dramatically in the past two weeks, with 52,000 peasants crossing the border since Dec. 16, according to the U.N. refugee agency. There are another 50,000 peasants "in the pipeline" that has been established between the famine-stricken Ethiopian highlands and Sudan, according to F. Allen Harris, director of the office of emergency operations for the State Department's Bureau of Refugee Programs.

In addition, another 200,000 to 400,000 peasants in Tigray Province, the most severely famine-blighted area of Ethiopia, are likely to flee towards Sudan in the next month, according to a Washington spokesman for the Relief Society of Tigray, an organization that operates in Tigray as an arm of the rebel movement there. The Tigray Peoples Liberation Front has been fighting the Ethiopian government for 10 years and is generally believed to control about 85 percent of the mountainous province.

"There is nothing left to eat in Tigray," Yared Berhe, a spokesman for the Tigray relief society, said yesterday. "If people stay, they will die."

According to a senior State Department official, who recently returned from a tour of the Sudanese refugee camps, peasants say they are fleeing Ethiopia both to find food and to escape the Ethiopian government's resettlement plan.

The Ethiopian government, in a scheme that it insists is strictly voluntary, has resettled more than 100,000 northern peasants in the past six weeks to more fertile lowland areas in southwest Ethiopia. Most of the peasants are loaded on trucks and buses at embarkation centers located near large famine-relief feeding camps in north central Ethiopia.

Western donor nations have criticized the resettlement plan as an expensive diversion of famine-relief resources that may be motivated as much by a government desire to depopulate the rebel-controlled north as by humantarian considerations. The Ethiopian government defends resettlement as the only alternative to mass starvation in a region where drought, erosion and bad farming practices have destroyed most of the arable land.

"The refugees said that -- next to the lack of food -- what drove them to Sudan was a fear that if they went to the Ethiopian government's feeding camps they would be resettled," the State Department official said.

Ethiopian government aircraft attacked fleeing Tigrayan peasants on Dec. 4, killing 18 people and injuring 53 others, according to Tekle Woint Assefu, a leader of the Tigray relief society. Tekle told a U.S. official in Sudan that two Soviet MiG fighter planes bombed a transit camp near the northern Ethiopian town of Shelallo.

Tekle arrived in a Sudanese refugee camp in mid-December with the 53 wounded refugees, most of whom were treated for shrapnel wounds by doctors from Medecins Sans Frontieres, a French voluntary organization.

The U.N. refugee agency has requested $11.8 million in relief aid for Ethiopians in eastern Sudan. The refugee agency has also requested funding to help meet refugee needs in western Sudan, where an estimated 100,000 Chadians crossed the border, fleeing drought in their central African nation.