Hundreds of half-starved peasants from drought-stricken regions of northern Ethiopia have begun crossing into Sudan in what some relief officials fear may be the start of an exodus involving tens of thousands.

The Ethiopian government and two opposition groups fighting in the provinces of Eritrea and Tigray say that the situation is "extremely serious," probably the most severe since a 1973-74 drought in the areas led to the death of an estimated 200,000 people.

Mark Bowden, an official of the British Save the Children Fund who recently completed a visit to Ethiopia, has warned that there is a "real risk" of famine for 3.5 million people living in the affected areas and that "tens of thousands of lives" are at stake.

Bowden told Reuter news agency in Nairobi, Kenya, that tens of thousands of people "with absolutely nothing" were coming to government-run relief centers.

Another outside witness, a sociology professor from Britain's Durham University who just spent three months in Tigray, gave a similar account. In a public report, Jon Bennett said he had seen "many hundreds moving westward" inside Tigray, "carrying only a few household possessions on their backs."

He said about 250 families per day were migrating from the most affected areas in the northeast and south toward the west, where there is still some food. Some 2,000 peasants had crossed into Sudan, he said.

Sudanese officials, already coping with 440,000 Ethiopian refugees and 170,000 Ugandans in the south, said they will not be able to deal with a large new influx of Ethiopians.

The Ethiopian government, the Tigray People's Liberation Front opposition group and the Eritrean People's Liberation Front are appealing for international assistance to stop an exodus into Sudan. But they disagree on how such aid should be distributed, with the opposition groups claiming that they control most of the areas where the drought-afflicted population lives and therefore it should go through them.

During the great drought of 1973-74, international relief agencies failed to respond because the late Ethiopian emperor Haile Selassie tried to cover up the disaster and barred access to the starving peasants. Today, only the Save the Children Fund appears to be mobilizing to help. One Washington-based group, the International Rescue Committee, has been winding down its activities here.

A spokesman for the State Department-supported committee, Jon Eklund, said in Washington that as a result of the reports from the drought area, "we are going to stay on" in Sudan. He said seven staff members are providing medical, sanitation and educational aid at four refugee camps.

The United Nations has not surveyed the likelihood of an influx of famine victims. Yet a U.N. High Commissioner for Refugees mission that visited here in November concluded that a contingency plan for emergency aid was needed "due to the uncertainty of the general situation."

The U.N. commissioner's representative in Khartoum, Robert Muller, said, "Everybody knows there is a problem in Ethiopia. Whether they the refugees will move or not move is a different problem." Muller said he was "certain" that the situation was worse than in the past two years.

Muller also said drought victims were not the concern of his office, because they were not classified officially as "refugees." The United Nations has a special disaster relief agency that deals with such emergencies, he said.

The U.N. commissioner's representative here, Peter Parr, seemed to agree with Muller that reports of a probable mass influx into Sudan were speculative. On the basis of information available, he said, "I would not say there is a terrible drought, certainly not enough to generate tens of thousands coming over. But it's worthwhile being prepared."

The U.N. High Commissioner for Refugees, for reasons that have nothing to do with the current drought in Ethiopia, is opening a center 40 miles northeast of here at Showat capable of receiving 5,000 refugees.

The U.N. agency's count of registered Ethiopian refugees shows a big jump to a monthly average of 300 to 400 starting last April, apparently because of bad weather and fighting in Tigray Province near Eritrea.

The start of an Ethiopian Army offensive to crush the Tigray People's Liberation Front guerrillas is likely to aggravate the situation. The Army is expected to try to seize the guerrillas' food supplies in the better-off western part of Tigray. If it succeeds, the numbers fleeing into Sudan seem certain to increase.

Ismael Ebrahim, the Sudanese assistant commissioner for refugees, said in an interview here that he thought the situation was "not as serious as the drought of 1973." But he added that "it's getting worse and worse as the food supply in western Tigray goes."

He said the Relief Society of Tigray, a group associated with the Tigray rebels, is trucking 400 tons of food into the province monthly to aid drought victims and trying to keep them from streaming into Sudan for help.

If this fails, he said, "thousands and thousands" of peasants would come across seeking assistance. "I don't think we have the capacity to cope with that." He said Sudanese grain stocks were low this year because of a poor harvest around Gedaref, which is the country's main agricultural center.

Ebrahim said 30 to 50 Ethiopians were arriving daily at his office seeking help and that 60 to 100 were drifting into Gedaref, while others were waiting at the border. Roughly 50 persons, mostly single men, could be seen waiting outside his office the day two U.S. reporters visited last month.

At Tawawa, a settlement outside Gedaref for Ethiopian refugees, a newly arrived Ethiopian, Gebre Amlak, 38, said he had walked for one month from his village near Makele, the Tigrayan provincial capital. He said he was seeking work and food in Sudan while his family was still at home.

He said that he and nine other men had traveled mostly by night because of the fighting in Tigray. He said they were trying to avoid being conscripted as soldiers by either side.

His account seemed to suggest that the motives for which Ethiopians are fleeing to Sudan have as much to do with the military situation as the drought. Thus whether they are technically "refugees" becomes a murky question, but the U.N. High Commissioner for Refugees is helping hundreds of Ethiopians like Amlak in Gedaref.